Autopep

This PR is branched off #17, so that should be merged first.

I started to apply Python 3 fixes (see #14), but then ran into [this](https://gist.github.com/cdeil/6223662) `TabError`.
So I decided to run `autopep8` first:
```
autopep8 -i --ignore E501,E126,E128,E225,E226,E231 -r pyvo scripts tests
```

@RayPlante Let me know if you're willing to merge this or if you prefer manual or fewer formatting changes.