Add recipe for vpython and its dependencies

@asmeurer -- this is the set of recipes discussed a couple months ago in this thread [1]. 

Most of it is straightforward except the boost recipe. My recollection was that the current boost recipe didn't work with vpython (or maybe I couldn't build it at all?), so I created a separate boost recipe in boost-vpython that builds only those pieces of boost needed for vpython.

Also pinging @brucesherwood and @sspickle because they are the primary maintainers of vpython itself (though I've appropriated responsibility for the conda recipe).

[1] https://groups.google.com/a/continuum.io/forum/#!searchin/anaconda/vpython/anaconda/6fraNlCpyDo/vS1A84g_gLYJ
Why do you have this?