Fix #444.  Handle "2 or more" arguments, rather than "2 or 3" arguments.  Fix the docstrings to reflect this.  By stricter in how extra kwargs are handled to minimize confusion.
Rename astropy.io.vo to astropy.io.votable
Add support for converting VOTable instances to/from astropy.table.Table instances.
Add warning about `to_table`
Make things more compatible with Numpy masked arrays.
Store the array in a single Numpy masked array.  Provide a "from_table" convenience function at the top level.
Remove outdated warning
Fix for Python 3
Fix typos.
Fix for Numpy 1.4.1
Fix docstring.
Update documentation for units to include some of the recent additions.
Address many of the items in PR #419.
Restore a warning about the mask being thrown away.
Merge pull request #444 from mdboom/wcs/flexible_arguments

Make it easier for users to convert >2 coordinates with WCS
Merge pull request #363 from mdboom/vo/table_support

Update astropy.io.vo to use the astropy.table.Table class
I got a traceback this morning when trying to run Astropy's setup.py (in order
to try to reproduce #452).  Instead I got something unrelated:

```
Traceback (most recent call last):
  File "./setup.py", line 25, in <module>
    from astropy import setup_helpers
  File "/bray/sc1/root/src/astropy/astropy/astropy/setup_helpers.py", line 196, in <module>
    from sphinx.setup_command import BuildDoc
  File "/bray/sc1/root/home/embray/.virtualenvs/astropy-dev-27/lib/python2.7/site-packages/sphinx/setup_command.py", line 20, in <module>
    from sphinx.application import Sphinx
  File "/bray/sc1/root/home/embray/.virtualenvs/astropy-dev-27/lib/python2.7/site-packages/sphinx/application.py", line 21, in <module>
    from docutils.parsers.rst import convert_directive_function, \
  File "/bray/sc1/root/home/embray/.virtualenvs/astropy-dev-27/lib/python2.7/site-packages/docutils/parsers/rst/__init__.py", line 75, in <module>
    from docutils.parsers.rst import states
  File "/bray/sc1/root/home/embray/.virtualenvs/astropy-dev-27/lib/python2.7/site-packages/docutils/parsers/rst/states.py", line 108, in <module>
    import roman
ImportError: No module named roman
```

The problem is that if importing sphinx fails it should be ignored, but if any
other ImportError occurs in the *process* of importing Sphinx it is raised.
There are a couple problems with this.  First of all searching for the string
`'sphinx'` in `e.args[0]` is an unreliable way to determine anything about an
ImportError (in fairness, there really is no good way prior to Python 3.3 which
finally fixed that wart).

Second of all, what actually happened here is that there's something broken
about my docutils installation.  Having a broken docutils or sphinx
installation should NOT cause Astropy installation to fail, since it's not even
necessary except for building the docs.  Allowing an error to be raised here
could easily lead to confusing, difficult to reproduce bug reports since it was
something broken in my setup, and nothing to do with Astropy.
Fixes #452. Don't assume the 'run' method is a direct member of the class, and not inherited through a parent class.  In fact, don't assume that a run method already exists at all (though it really always should if it it's a distutils command).
Clarified a comment
Instead of wrapping the entire AstropyBuildSphinx definition in a try/except block, add a HAVE_SPHINX global variable a la HAVE_CYTHON; put the AstropyBuildSphinx definition in an if statement instead.