openSCAD print anchors

Some users have found that the rafts generated by common toolpath generators are wasteful of material and difficult to remove. cptnAWESOME found that it is easier to add raft-like features to .stl files prior to passing them to a toolpath generator, as in http://www.thingiverse.com/thing:16596.

This script performs this function automatically and uniformly, so that designers can distribute files in a form that is as machine- and technology-independent as possible. The user can then apply whatever preprocesseing steps are necessary to ensure the best print characteristics on her machine.