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.
Little nitpick: I would make 10000 into a variable and use that variable in your code:
```.js
var maxTimeout = 10000;

if (timeout > maxTimeout) { 
  console.warn("SCT timeout value too large. Setting to maximum value:", maxTimeout);
  timeout = maxTimeout;
}
```