Switching to platformIO

I think it will be a good think to move from ArduinoIDE to PlatforIO.

The depencies management is a lot better and i think it will be easier for user to build and flash the card with PlatformIO.

It also support natively the esp32.

Instructions for platformio:

Create a top level directory with these subdirectories: include/ lib/ .pio/ src/ test/

Put the contents of the grbl_controller_esp32 source tree in the src/ subdirectory. Create a "platformio.ini" file in the top level directory with these contents:

[env:esp32dev]
platform = espressif32
board = esp32dev
framework = arduino
lib_extra_dirs = ~/Documents/Arduino/libraries
lib_deps =
 SdFat
src_filter =
    +<*.h> +<*.s> +<*.S> +<*.cpp> +<*.c> +<*.ino> +<src/>
    -<.git/> -<data/> -<test/> -<tests/> -<Fonts/> -<Extensions/>
upload_speed = 921600
monitor_speed = 115200
monitor_flags =
	--filter=esp32_exception_decoder