Added new serial class, remove interrupt chaining

The new RawSerial class is a simple wrapper over the serial HAL that can
be safely used from an interrupt handler.
Interrupt chaining code was removed from InterruptIn, Serial and Ticker
because it caused lots of issues with the RTOS. Interrupt chaining is
still possible using the InterruptManager class.

Merge pull request ARMmbed#72 from jorisa/master

Split uVision project source files in groups mbed/hal/src

Official release 66 of the mbed library

Official mbed library build 65