added serial mouse driver for Microsoft and Mousesystems mice

 * Both drivers use the interface defined in serial_mouse.h
 * They should work with any UART implementation (hardware/software UART)
 * The Microsoft driver is currently untested.
   The Mousesystems driver is confirmed to work.
fixed PS/2 keyboard converter config

When using the PS/2 interrupt implementation, the DATA pin should be
PD0 as the documentation (README.md) states.
integrated serial mouse drivers as a feature into the firmware architecture

 * can be enabled by defining Makefile macro SERIAL_MOUSE_MICROSOFT_ENABLE or
   SERIAL_MOUSE_MOUSESYSTEMS_ENABLE.
 * Serial implementation can be chosen via SERIAL_MOUSE_USE_SOFT and
   SERIAL_MOUSE_USE_UART macros
 * UART configuration still has to be done in config.h: I added working clauses
   for both mouse protocols to ps2_usb's config.h
factored out serial_mouse_init() into serial_mouse.h
serial_mouse: simplified clipping of X/Y/V/H changes below -127 using a MAX macro
updated copyrights: serial_mouse.h, serial_mouse_microsoft.c and serial_mouse_mousesystems.c are new
Add keyboard/mbed_onekey
Port timer to mbed
Fix print and timer
Port action_* to mbed
Fix debug.h and remove debug_config.h
Fix common files for mbed
Fix build files for mbed
Port ps2_usb to mbed
Add LED indicator support in mbed
Add checksum tool for NXP LPC
Merge branch 'mbed' into dev
Port action_* to mbed
Fix timer.h to include AVR specific header
Fix for new API(key_t to keypos_t)