rpmify with Python

RPMify is re-coded from Dave Durant's RPMify for C# (windows only) from:
http://www.thingiverse.com/thing:4407

This version uses python instead and can be run on any platform

The call is "python RPMify.py FILE.gcode MAXRPM"
Where FILE.gcode is the complete path and gcode you want to RPMify and MAXRPM is the maximum RPM you want to run, such as 20.

The goal is to process your gcode file one line at a time and replace PWM with RPM
M108 S255 --> M108 R20.0