Simple Snap-Fit Joints Library

This is a simple snap-fit joints library based on "Snap-Fit Joints for Plastics - A Design Guide" by Bayer MaterialScience LLC .
http://fab.cba.mit.edu/classes/S62.12/people/vernelle.noel/Plastic_Snap_fit_design.pdf

The idea is to correctly dimension the snap-fit joints, according to the elongation at break that can withstand.
-The global variable eps define the material (e.g. PLA: eps=0.03; ABS: eps=0.06)
-The dimension are the same reported on Design Guide. For simple cantilever snap it is also possible to define h or y (see figure)
-The value of K2 or K1 used in Ring snap could be taken from Fig 10 of guide (but the default K=2 should be ok).

I have also added some simple example on the use of the library. I also printed the cable clamp, and it works well.
it is suggested to print snap-fit cantilever on the XY printer plane.

New version : 0.36
added SnapHoleY module

Bug Fix: 0.35
on the basis of the shanemgrey reporting:
on RSnapY I have added a check to avioid