Note previous belt lengths were incorrect with negative turns.
Fixed spelling typos.
_belt_length() no longer needs belt type.
Uptated images and readme.
Can now:
- render open loops
- twist the belt
- use pulleys instead of radius in the points list
Fixes some precision a few places
Breaking change in belt_length(); now requires a type argument
Moved screw_insert() from inserts.scad to screw.scad.
Changed most includes of inserts.scad to use insert.scad.
Removed linear_bearings, iecs, rockers and microswitches from lib.scad as
already included by other vitamins.
