MCU library for various AVR microcontrollers and others.
Add this as a sub module to your exsiting MCU project repository:
git submodule add https://github.com/LilyTronics/lily_mcu_lib [<path>]
By default the sub module is cloned in lily_mcu_lib. This can be overridden by the <path> parameter.
Commit the newly added submodule.