Remix of split X-Ends

this is a remix of Enif's design: http://www.thingiverse.com/thing:514582

It is my first attempt at OpenSCAD, hence not perfect, but it works (already printed a set).

My changes:
1) Added leadscrew support with a variable : Leadscrew = True or False
2) Dimensions of the LS can be entered and also the position of the fixation holes of the leadscrew nut can be adjusted (angle)
3) Added a selection of bearings LM8uu, LM10uu and LM12uu, so that it can be used for the Mega Prusa as well
4)