Added serial printf support

For now there's no float support. Converted the basic commands, and
partially converted the api.
Much leaner printf implementation

Reusing existing num to/from string conversion methods
Added -ansi flag to compiler options

Otherwise get compile error with cppunit (64 bit compilation for 32 bit
target)
Added unit test for serial_printf

Currently supporting characters, unsigned int, int, straight strings.
Not supporting hex, floats, doubles, left/right align or 0 align
Removed unused printf field in serial structure
Merge remote-tracking branch 'origin/serial_printf_test'