Fix multiple definition errors when using library header in two different files

[maxgerhardt]

Since this library defines the Breakout object in its header file, it's a death sentence for users wanting to use the header file from two different .cpp files, as such is common in IDEs like PlatformIO + VSCode, since that causes multiple definition of errors.

Users are running into this error for example here.

This PR fixes this error by only declaring the breakout object to be extern and then adding a .cpp file in which the object is then created once.

[github-actions]

Memory usage change @ a3ffef2

Board	flash	%	RAM for global variables	%
arduino:mbed_portenta:envie_m7	N/A	N/A	N/A	N/A

Click for full report table

Board	examples/BreakoutRTCGet flash	%	examples/BreakoutRTCGet RAM for global variables	%	examples/BreakoutRTCSet flash	%	examples/BreakoutRTCSet RAM for global variables	%	examples/BreakoutWebServer flash	%	examples/BreakoutWebServer RAM for global variables	%	examples/GpioManagement flash	%	examples/GpioManagement RAM for global variables	%	examples/LM75BTemperature flash	%	examples/LM75BTemperature RAM for global variables	%	examples/PDMRootMeanSquare flash	%	examples/PDMRootMeanSquare RAM for global variables	%	examples/analogRead flash	%	examples/analogRead RAM for global variables	%	examples/analogWrite flash	%	examples/analogWrite RAM for global variables	%
arduino:mbed_portenta:envie_m7	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A

Click for full report CSV

Board,examples/BreakoutRTCGet<br>flash,%,examples/BreakoutRTCGet<br>RAM for global variables,%,examples/BreakoutRTCSet<br>flash,%,examples/BreakoutRTCSet<br>RAM for global variables,%,examples/BreakoutWebServer<br>flash,%,examples/BreakoutWebServer<br>RAM for global variables,%,examples/GpioManagement<br>flash,%,examples/GpioManagement<br>RAM for global variables,%,examples/LM75BTemperature<br>flash,%,examples/LM75BTemperature<br>RAM for global variables,%,examples/PDMRootMeanSquare<br>flash,%,examples/PDMRootMeanSquare<br>RAM for global variables,%,examples/analogRead<br>flash,%,examples/analogRead<br>RAM for global variables,%,examples/analogWrite<br>flash,%,examples/analogWrite<br>RAM for global variables,%
arduino:mbed_portenta:envie_m7,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A

[aentinger]

LGTM 👍