Refactor splatalogue

This is a complete rewrite of splatalogue, based more off of http://agpy.googlecode.com/svn/trunk/agpy/query_splatalogue.py than the `mechanize` version.

It provides an interface that resembles the splatalogue web interface, NOT a fully functional VO-enabled SLAP interface.  The latter is possible, but the documentation seems to be presently unavailable, so we cannot support that interface.

This doesn't fully conform to the astroquery API, but it goes most of the way.  

There are still problems with docstrings not being inherited properly.

This depends on PR #149