added hexbit driver vitamin


created a parametric hexagon for making bit driver subtraction in the
hex bit adapter
added servo motor screw

added a separate motor screw vitamin based on the small hi low screw.
This will work with the hex bit adapter
added tolerance to motorscrew
added tolerance to hex bit
parameterized motor screw variables
turned motor screw parameters into functions

motor screw params now have prefix 'MS' and are functions.