OpenSCAD library: pie

An OpenSCAD library addition for generating twodimensional pies (circle sectors), specified by radius and angle. Zero degree lines is vertical, increasing angles count clockwise: 90 degrees is the 3 o'clock position, 270 degrees the 9 o'clock position.
This is a slightly shorter and more efficient rewrite of an earlier version.

Added rather short versions of limited pie modules, usable for pies from 0 to 90 degree (pie90) or 0 to 180 degree (pie180) angles.