Simple Rack & Pinion 003

I used Sasa's excellent Simple Rack & Pinion script in my own MIni-CNC "http://www.thingiverse.com/thing:185925" with a few very minor modifications. They are as follows:

1) Rather than using an approximation of pi, I included the OpenSCAD constant, PI in the calculations.
2) I added three mathematical functions which would help the user easily figure out the pitch radius, outer radius, and the radius that would be used to calculate/approximate the distance traveled

Otherwise, my versi