* 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

Properly follow ternary else() chain, help out by pre-pending if()
Resolve #2239, thanks to @sigmafx

- 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

https://github.com/xoseperez/espurna/pull/1772#issuecomment-609847420
> Without the patch btnRepDel overrides every btnRepDel0, btnRepDel1 etc., btnRepDel0 read second, then hard-coded value.
With the patch btnRepDel0 is read first, then btnRepDel, then hard-coded value.

Indexed key can only be set via settings upload or in terminal, WebUI can change only the global override setting. Allow more 'specific' key to override global setting.

* mqtt: enum state

* mqtt: async client buffer with MQTT_MAX_PACKET_SIZE

* mqtt: rework debug messages

* mqtt: MQTT_BUFFER_MAX_SIZE

* mqtt/test: debug log for async callback

* mqtt/test: don't log things we don't handle

* button: fix typo

In case board configuration is empty, loop should try to check at least once

* wip

* cleanup buttons-through-serial code, remove hw mention from button module

* remove wip

* implement mqtt settings

* fixup struct members, dual no longer allocates debouncer

* add missing debounceevent lib

* fix missing event_handler, update names

* fix namespace

* drop lib

* fix int<->bool comparison

* Move gpio16 handling from DigitalPin to EventHandler

* Cleanup debounceevent headers

* Don't expect system headers to be included

* re 70b54c489f - no allocation, for real

* Adjust settings names

* dont retain by default

* unused

* typo

* Fix length type (ref 6017ad9474)

* Move pin class outside of debounce lib, lowercase ns

* move event handling inside of button_t

* refactor config. ..._MODE -> _CONFIG, ..._MODE_... -> ..._ACTION_...

* fix test

* naming

* move indexed value to header

* refactor actions into direct opts

* fix webui, fix buttons not respecting old user setting

* change button config format from bitmask to a struct, adjust settings conversion

* proxy some more header defautls, fix web kv

* gpiopin

* adjust webui func to support every setting

* clarify single-return event->string

* fix dual setting

* fix dual packet condition, de-duplicate funcs

* fix bogus warning

* Fixes and updates for thermostat and display:

- Switch to original esp8266-oled-ssd1306 library
- Fixes and updates for thermostat and display
- Add display switching off after interval
- If THERMOSTAT_DISPLAY_SUPPORT enabled, then one click enable display, long click switch relay. This functionality also depend on fix for long click. See pull request https://github.com/xoseperez/espurna/pull/2172

* Move buttons definitions for display to dependencies.h

* Pin ThingPulse/esp8266-oled-ssd1306#3398c97

- use similar to relay & wifi, configuration through helper methods that
  use indexed defines
- clock cycles for led delay polling
- button mode defaults

* 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

- mask is defined as (relay# status << number)
- transparently handle base-2 and base-10 numbers
- if the relay mode requires us to save the mask, it will be saved as base-2

- update every dynamicjsonbuffer with fixed size constructor argument
- change to ws callback registration to use a class builder (just cosmetic)
- test multiple ws data callbacks for each module
- remove some of the static strings in favour of ws data callback
- improve sensor ws callback data size, remove duplicated strings
- use static buffer in wsDebugSend
- postpone wsSend until loop, implement wsPost to allow other modules to queue message callbacks. remove Ticker based ws callbacks for data
- update WebUI files