Added Parallel tool + command processing.

 - Added command line processor
 - Added Basic Units to structs.h
 - Fixed Parallel tool to actually do something

The Parallel tool utilizes the command line processor to alter its
parameters; currently it only works with lines, circles, and arcs.
This will also be used for such things as the Polygon tool and probably
lots of others; it will also probably be used to make it so that object
primitives can be added via the command line.