Side button support

[docprofsky]

The two side buttons are not supported in software. These would be good for setting the time with the keypad and allowing app switching without needing a key on the keypad.

According to the schematic, P1.5 is the mode button (raised) and P1.6 is the set button (recessed).

[travisgoodspeed]

Will do. These buttons are also the serial port for the bootloader, so I'll be adding key combos for emulating them using just the keypad.

[travisgoodspeed]

The mode button now works to change modes, freeing up the face buttons. Press / and * to emulate Mode and + and - to emulate Set. Mode cycles through the applications, and Set will be used for application-specific functions.

Key scanning has also been sped up by testing for a press and only scanning if one is known to exist.