Change the underlying command line handling:
- switch to a custom parser, inspired by redis / sds
- update terminalRegisterCommand signature, pass only bare minimum
- clean-up `help` & `commands`. update settings `set`, `get` and `del`
- allow our custom test suite to run command-line tests
- clean-up Stream IO to allow us to print large things into debug stream (for example, `eeprom.dump`)
- send parsing errors to the debug log

As a proof of concept, introduce `TERMINAL_MQTT_SUPPORT` and `TERMINAL_WEB_API_SUPPORT`
- MQTT subscribes to the `<root>/cmd/set` and sends response to the `<root>/cmd`. We can't output too much, as we don't have any large-send API.
- Web API listens to the `/api/cmd?apikey=...&line=...` (or PUT, params inside the body). This one is intended as a possible replacement of the `API_SUPPORT`. Internals introduce a 'task' around the AsyncWebServerRequest object that will simulate what WiFiClient does and push data into it continuously, switching between CONT and SYS.

Both are experimental. We only accept a single command and not every command is updated to use Print `ctx.output` object. We are also somewhat limited by the Print / Stream overall, perhaps I am overestimating the usefulness of Arduino compatibility to such an extent :)
Web API handler can also sometimes show only part of the result, whenever the command tries to yield() by itself waiting for something. Perhaps we would need to create a custom request handler for that specific use-case.

* emon: configure ratios without reboot

* settings: serialize() support

* debug: use vsnprintf from newlib, not from sdk

* settings/experimental: show defaults via `get`

* emon: override base methods, fix defaults

* sensor/emon: expose internal index calculation

- refactor configuration to use the correct index when accessing indexed
  sensor methods. store index value on magnitude, refactor loops to
  accomodate this new functionality
- rename slot(index) -> description(index), since we use 'slot' as
  numeric value

- general conversion from .ino modules into a separate .cpp files
- clean-up internal headers, place libraries into .h. guard .cpp with _SUPPORT flags 
- fix some instances of shared variables instead of public methods
- tweak build system to still build a single source file via os environment variable ESPURNA_BUILD_SINGLE_SOURCE

* hlw8012: load hardware-specific ratios
* hlw8012: read energy in pre() callback
* dcz: nvalue should be integer
* sns: fix pressure constrain
* sns: load ratios based on index too
* sns: per-magnitude corrections (still limited by type)
* sns: attach units to index

* ADC_VCC is not macro

* In esp.h ADC_VCC and ADC_TOUT is not macro, so define macro.

* ADC_VCC and ADC_TOUT fixes in utils.ino and sensors.h

* Adding support for I2C temperature and humidity sensor HDC1080 / 831R

* Added HDC1080 to test\build\sensor.h and arduino.h

* added brackets

* Revert ADC_MODE_VALUE to initial values

* Eof newline

* Eof newline

Co-authored-by: Max Prokhorov <prokhorov.max@outlook.com>

Co-authored-by: Joop Hilverink <33230021+HilverinkJ@users.noreply.github.com>

- Update sensor classes to support a generic way to store energy values
- Update sensor conversion code to deal with units and not magnitudes
- Add magnitude<->unit for sensors, generic way of defining used unit. Convert from sensor magnitude unit to the one used for display.
- Reset energy value based on index through external means (MQTT, HTTP)
- Rework energy timestamping, update webui with 'last saved' value

While this solves the energy conversion issues and we are finally seeing the real value, what I don't really like:
- KilowattHour and WattHour are separate enum tags, thus sort-of are different types altogether
- Conversion code in Energy object should probably use some generic 'ratio' calculation? (https://en.cppreference.com/w/cpp/numeric/ratio/ratio)
- We are still using runtime checks to do calculations and depend that sensor outputs only one specific value type.

Consider this a fix for energy display / storage and preliminary work on sensor.ino
Further sensor refactoring... soon.

* Add support for read PIO-A of DS2406

* Verify reset() reseult

* Sensors: refactor configuration

- move sensor implementaion to the .ino,
  remove dependency undef / define from sensor files
- update test/build/sensor.h from SENSOR_SUPPORT
- allow to change sensor config variables externally
- `#include <...>` for global headers and libraries,
  fix relative path for math library

* add missing sns <-> i2c dependency

* ledrelay should return relay_none as default

* rollback to original test header

* include debug header when requested (relative)

* experimental: refactor get/set/del/hasSetting

* sensors

* lights

* cleaup

* r

* tuya

* fixup! sensors

* fixup! tuya

* header defaults types

* fix lights

* setup already checks for max

* helper for flashstring

* fix overload

* oops

* refactor includes

* warnings

* test with migrate

* add ids in a separate file

* cleanup

rev: crash

rev: domoticz

rev: encoder

rev: loopdelay

rev: hass

rev: i2c

rev2: hass

rev: mqtt

rev: rfm69

rev: relay

rev: rpn

rev: settings setup

rev: hb settings

rev: telnet preprocessor fix

rev: settings wrap

rev: tspk bool style

rev: wifi types

rev: util hb

rev: settings

fixup! rev: settings

* rev: cleanup wifi injections based on new getters

* hasSetting now can return true for empty key

* show hardcoded network in web

* oops

* fix ws referencing wrong index

* ensure empty strings are written

* c/p

* use experimental schema style for payload, mark network as not deletable

* allow to customize converter

* shorter syntax, try using with wifi

* use proper #if syntax to handle definitions that are missing

* fixup ota sc checks getter, cast schEnabled to bool

* add utils header to sensors

* sensor: add DHT_CHIP_SI7021 references

* sensor: update DHT_TYPE definitions, use enum

* changelog

Operating specifications / Communication and signal

"Data-bus's free status is high voltage level. When communication
between MCU and DHT22 begin, program of MCU will transform data-bus's
voltage level from high to low level and this process must beyond at least
**1ms** to ensure DHT22 could detect MCU's signal, then MCU will wait 20-40us for
DHT22's response."

* Added T6613

* Added T6613

* Added T6613

* Added T6613

* Added T6613

* Added T6613

* Added T6613

* Added T6613

* Added T6613

* Updated copyright string

* Buffer from 6 bytes to 8 bytes

Current gcc-4 does not mark this as warning, but gcc-9 notices the 3 char size requirement. Buffer should be 8

* Use 5000ppm max

* Add Shelly 2.5

* Add ADE7953 sensor support

* Fix compilation

* Use only one instance

* WIP: Not working, I got StoreProhibited exception

* Fix exception

* Fix merge issues

* Apply request review changes

* declare struct before using it

* uninterruptible delay

* try optimized reg_size

* fix types

* Remove gpio 0 input in analog sensor

* Add energy to ADE7953, it is not finished yet

* Add new method to save energy with index

* Finish energy for ADE7953

Thanks to @tonilopezmr 
1c3d68af34

* Core 2.6.0+ fixes

* fix env -> config, run travis04 job

* don't duplicate free heap in frag data, use single stats struct

* fix dtostrf warnings, bump buffer sizes

* ...and even less words for fragmentation stat

* enable multiple Digital, Events & PulseMeter

* delete SPI dependency

* back to only one PulseMeter

* deprecared pins

- cache ms<->clockcycles conversions
- move callback invocation outside of ISR handler
- remember last event value

- dynamic number and address setting
- do not return i2c-specific error for wrong values

* Add reactive power calculation and bring output to in line with HLW8012 sensor based units

* Update CSE7766Sensor.h

* Fix energy ratio input for pulse meter sensor

* checkout origin/dev -- webui files

* Testing branch

* Added ability (by define) to scale analog sensor, also with number of decimals (it was formerly zero)
Useful when running on batteries to check the battery voltage just 
adding the appropriate resistor

* Reverting DHTSensor.h file

* Trying again to revert DHTSensor.h

* Using macro DEBUG_MSG

* fix method types

* Testing branch

* Added ability (by define) to scale analog sensor, also with number of decimals (it was formerly zero)
Useful when running on batteries to check the battery voltage just 
adding the appropriate resistor

* Reverting DHTSensor.h file

* Trying again to revert DHTSensor.h

* Using macro DEBUG_MSG

* fix method types