hub75: begin porting logic from pico-examples

[soypat]

Looks to solve https://github.com/tinygo-org/pio/issues/7

@deadprogram do you think you can take it from here?

Note: I did notice something odd in the usage of the StateMachine.Exec method and left a comment. They apparently pass in a offset/position instead of an instruction, which I think is undefined behaviour?