Incorporate strap mount into walls.

Also required widening the sides to allow the straps to be in-line.
Lengthen the optic slider slots.
Build all STLs.
Build in some suppport material for strap mounts.
Try with a little more support.
Back to two supports.

Two worked slightly better than three and requires less post-processing.
Grab config from optics test.
Restore sloped version of strap mount for variants

The A and B variants can only be made to work with the slope-sided
version of the strap mount. The sides are too narrow otherwise.
Refactor to remove redundant code.
Cleanup internal docs and generate STLs.

Documented the new modules in visor_body.
Generate STLs.
Merge branch 'new_straps'

Conflicts:
	visor-A.stl
	visor-B.stl
	visor-C.stl
	visor-assembled.stl
	visor.scad
Update STLs after merge.