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.
Update Cortex SysTick for libperipha.
Add enable(), disable(), altfunc() methods.
Add basic (UART0 block) LM4 UART implementation.
Stellaris Launchpad supported.
Mention docs/ dir.
Drop gpio_stm32_opencm3.hpp - makes no sense to maintain.
Elaborate GPIO class hierarcht - introduce PortPin.

IPin is completely abstracted pin without constrains of belonging to
anything. PinPort is a pin which explicitly belongs to a port and
has specific bit position in it.
Make width part of IPort and add more methods to it.
IPin is the most basic notion, put it at the top.