Added support for "backsided" objects.

This essentially adds support for front-face culling as opposed to the
usual back-face culling. This will result in all front-facing polygons
to be culled and reveal the polygons on the "backside".
Merge pull request #399 from AndrewJo/master

Support for different cull modes
Fixed facet bug when front-face culling is used

When front-face culling is used, front-facing polygons were incorrectly
assumed to be counter clockwise.
Merge pull request #400 from AndrewJo/master

Fixed polygon facet bug for front-face culling mode