Added faceplate mounting holes for MY6812 motor module.
Modified galvanized_angle_1 module to support having an odd number of
holes in a given length.
Various useful components for drive trains.
Moved dune buggy chain tensioner arm to a separate module to allow
accurate modeling of disassembled tensioner.
Added a model of a 4" corner brace part.
Created separate model for chain tensioner spring.

Added more detail to 55 tooth sprocket.

Added documentary comments.
Add power cord to MY6812 motor model.

Minor improvements to comments.
Added the following modules:
* 2_and_half_inch_metal_u_strap
* tie_plate

Also improved various comments and made other minor formatting fixes.