More Flexible Pin Triggers

[betabrain]

Is your feature request related to a problem? Please describe.
Some boards have builtin buttons that pull pins low. Currently the pin triggers execute when the pin is high.

Describe the solution you'd like
I would like to be able to specify pin triggers that are edge triggered, and whether the edge is falling or raising.
Any setup required to set the pin up to work correctly, e.g. enable a pull up resistor, should also be possible.