Added a uart write method for integers

it is a bit rudimentary but it will do for now.
Added some pwm testing stuff

Specifically, some properties are now outputted and it runs a test of
some sawtooth waves where it counts how much time is left after every
output. Kind of a silly test right now as the output takes pretty much
no work, meaning it always has the full 20µs left. The idea is to expand
upon it when I introduce the wavetable stuff to see how much time that
takes.