Began integration of MCAD library:
  Replaced standalone functions.scad with versions from MCAD and deleted
  Included MCAD library files (linear_bearing.scad, stepper.scad) into design
Merged metric.scad into configuration.scad and deleted
Move static configuration parameters from wallace.scad to configuration.scad
Removed redundant configuration variables (rod_size, m3_size, etc.)
Began clean up of rod_size to differentiate between threaded_rod_diameter and smooth_bar_diameter
Include nophead's leadscrew coupler from Prusa Mendel i2