Support the STL format for 3D printing

[ftomassetti]

It would be AMAZING to be able to print 3D models of the generated world. To do that we could support the STL format: http://python-stl.readthedocs.io/en/latest/

[psi29a]

👍

[psi29a]

Found this:
https://pypi.python.org/pypi/numpy-stl

We can dump what is in Numpy to STL, then dump to file! :)