Parametric pulley - as a module

thingiverse

Remixed *the original* to able to use pulley generator in code like that: ``` use <./pulleys/pulley.scad> pulley ( "T2.5" , 25 , 0.7 , 1.678 ); ``` This enables us to i.e. translate the thing in the openscad easilly. *NOTE*: _ original build with include<> is still available, use `use` for mixing in other openscad files_ In next steps I'll move the two magic numbers out of function too and put on github for easier update.