[WIP] I/O and matrix update

[jackhumbert]

This is an attempt to introduce standard ways of reading from/writing to pins with these functions, where p is a pin like B4:

PIN_VALUE(p) // input at p - should be read as true or false
DDR_OUTPUT(p) // set p to output
DDR_INPUT(p) // set p to input
PORT_HIGH(p) // set p to high / 1
PORT_LOW(p)  // set p to low / 0

[jackhumbert]

Implemented in #3968.