Created demos of multiple libraries
Created layout directory and populated with:
  array.scad
  layouts.scad
  multiply.scad
Added rack_and_pinion.scad from http://www.thingiverse.com/thing:172508
Added to general/constants.scad:
  const_pi_div_180
  const_180_div_pi
Created shapes directory and populated with:
  2Dshapes.scad
  3d_triangle.scad
  boxes.scad
  lib.scad
  libtriangles.scad
  regular_shapes.scad
  rounder.scad
  shapes.scad
  standard_shapes.scad
  triangles.scad
  trochoids.scad
Moved metric_fasteners.scad and nuts_and_bolts.scad from hardware/ to fasteners/