Add Oskar Linde's hull()

[revarbat]

Add Oskar Linde's hull()

[adrianVmariano]

I suggest adding hull() as part of polyhedra.scad. We might want a secondary file to keep the namespace clean, as hull() depends on a ton of stuff we probably don't want exposed. I also think there should be some convention for functions that we're too lazy to actually hide but which aren't intended for users to call, maybe prefixing with "_" or something like that.

[revarbat]

Agreed on the _ prefix for non-exposed functions.

[adrianVmariano]

Perhaps we should rename it hull_faces() since it actually returns a face list.

There is discussion on the forum of doing a hull of points by calling the hull module on a bogus polyhedron with a vertex list and a list of garbage faces that includes all the vertices. Apparently this outperforms Linde's code, though of course you don't get a face list to work with.

[revarbat]

Working on integrating the common functions into the math library.

[revarbat]

Added in master branch commit 96739c3