Add a "pressed" function to support keyboard polling.

[davidbau]

Usage:

if pressed 'A' then write 'the A key is pressed.' if pressed 'control' then write 'the Control key is pressed.' write 'All pressed keys: ' + pressed.list().join(',')

It handles chording and resets tracked state when focus is lost.

[davidbau]

I'm preparing this change to make it easier to make keyboard-based games.

You can poll the left-arrow-key (for example) by testing

if pressed 'left' then write 'Left is pressed'

[ericfs]

API looks nice. Please let me know if you get this in before class.

[davidbau]

OK, I've updated based on your changes, and i'm merging to master. Thanks for the code review!