OpenSCAD Hairizer Multimaterial Version

This is a very small addition to Magonegro's excellent [Hairizer](https://www.thingiverse.com/thing:2306455) OpenSCAD script, which is used to create hairy models like the famous [Hairy Lion](https://www.thingiverse.com/thing:2007221) by _primoz_.

See the Lion thing for more info on printing and, uh...hairdressing...the resulting models. This script takes an existing STL file as input and creates a hairier version of it.

The original version of the script just outputs everything as one STL which is great for single-material printing but suboptimal for dual extrusion. This version has 3 modules. You basically just pick which of the three lines at the top to uncomment.
- HairyModel() is the original behavior of outputting everything as one file.
- Hair() creates only the hair and sacrificial cylinder.
- HoleyModel() creates a version of the original model with holes punched in it for the hair to pass through.

For a single-filament print you can just leave the Modules section alone