Added Pulsing LED Feature

Added: pulse, pulse_loop, pulse_all, pulse_arm functions.

Usage: 
```pulse([led], [brightness], [speed])
pulse_all([brightness], [speed])
pulse_arm([arm], [brightness], [speed])```

Brightness and LED are the same as in the base library, speed is an integer value where bigger numbers = faster pulse. Try 500 for a default. Tests are located in pulsetest.py