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.
Don't throw away bits. You want to expose the full resolution.

Pass the `pulse_time` in timer ticks to the event, and have it convert to fractional milliseconds as a double.