Parametric Shaft Coupling

Similar to http://www.thingiverse.com/thing:7153 but many parameters. Defaults are a 5mm to 7.8mm shaft which is what I measured on my machine. I got rid of the cut on one side as that led to slightly uneven pressure inducing a bit of wobble. In this model you can change: shaft diameters, bolt sizes, washers (if used), nut traps, and overall dimensions. This will make a strong shaft coupling without using much plastic. The code also makes a cleaner stl then my previous coupling.