Pin.readPulse() functionality

Basically does exactly what the title says. It implements readPulse functionality.

Check out `test/test_read_pulse.js` and mess around with the test to see if it's all good.

Comment/critique to your hearts desire.
I believe Kevin may have made this comment already, but you'll want to move the event listener after the `sct_read_pulse` call. If the sct status indicates an error getting started, then you will have an extra event listener attached to the complete event.