Add support for latexing array quantities

See #2258 for context - this makes it so that array quantities produce decent-looking latex output for ipython notebook consumption.

Look good to you in concept, @mdboom and @mhvk?  If so, I can add tests to check this properly
sure, although it ended up more natural to break it after 100 (not too ambiguous even though it's not precsiely PEP8-ish).  Will push that up and then merge.  

And thanks for all the feedback!