Add basic Stellaris Launchpad board header.
Rename board_launchpad.hpp -> board_launchpad_msp430.hpp
Refactor Cortex-M CPU classes to inherit from base class.
Add default Cortex-M CPU definition.
Add LM4 GPIO class.
Add Stellaris Launchpad board.
Add "lm4" target.
Add LM4 definition includes.
Rename stm32_includes.hpp for prefix sorting.