Docs Makefile additions, compute/numpy tests.

Fixes the problem of capabilities.py failing to create the graph the first time docs are built on a machine. Simple fix. Also, there are some tests and random changes to compute_numpy in here that I added in. Going to remove the other pull request. @mrocklin @cpcloud 
I'll change this. I guess i just have a different understanding of 'readability'. In my own code I usually try to really stay away from dense, one-line statements (not to say that this statement is particularly dense), preferring to list everything out in clearly named steps. That's just my intuition 

I'll keep this in mind.