RFC - use various core packages drectly instead of platformio-pkg-framework-arduinoavr

[liebman]

This is meant to start a discussion.

Has there been any thought about using the various cores (tiny, Mighty, Mega, Mini, etc) directly rather than having to copy files from the various repos or tar-files into platformio-pkg-framework-arduinoavr? This would certainly make updates cleaner and allow overriding each package easily in platformio.ini files.