Added new "primitive" shape modules, used them in upperCornerBrackets.scad
Added starter GantryEnd.scad

not parametrized, could use nut traps and a better attachment mechanism than press-fit
Added a nut trap module - hexagon and clearance hole.

Currently m3 only, should be parametrized for different screw specs.
Added holes to Bottom Bracket.scad, beefed up and widened GantryEnd.scad
Flattened to match 10mm axis center separation, added mount on back for tantillus-style screw
Made 608 mount conical for better printability
Set ymotor true to generate uniform upper corner brackets, added baseScrewOffset to simplify math, handled a case where holes were generated intersecting the edge of the part
Changed XYSpacing yet again
Gantry ends using sleeve bushings rather than igubal bearings
Merge pull request #2 from rdmarsh-cmu/master

this week's changes