sorted in a reverse order of when they were called
refactor gpio module itself, so our `namespace { ... }` stays consistent

using GCC `__builtin_{LINE,FILE,FUNC}()`
https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#index-_005f_005fbuiltin_005fLINE
https://en.cppreference.com/w/cpp/utility/source_location

Make the buffer work on '\n' instead of a limit, flush asap.
Still using single 'DEBUG' output for both terminal and debug prints;
we no longer have 'pre' and 'msg' distinction - there is just 'msg'.

Make every available call site 'private'
e.g. typing command in telnet no longer prints to serial or WebUI

Serial input is now optional, see `TERMINAL_SERIAL_SUPPORT`.
Telnet using async server is a proper Print implementation now.
WebUI, MQTT and HTTP input is allowed to inject multiple lines at once.

Modernize our helper classes and remove legacy 2.3.0 quirks.
Replace global Terminal object and allow to separately
split, parse ARGV list and perform command search and invocation with
standalone function calls.
(but, notice that we still depend on a globally shared 'commands' list)

This greatly reduces used RAM (but, slightly increases our ROM).

Update our test suite to use namespaces and new calling convention.

make our string comparisons nicer
also clean-up namespaces for storage access

rework more namespaces to use `espurna` root
makes internal references much easier (and shorter)

view class is not specific to settings, could use it across the app
remove duplicate code from IR