Results of the Documentation sprint

This is a PR to merge the feature branch from the documentation sprint into master. There are a few things that are blocking this and they are listed below.

ToDo:

- [x] Complete the API docs (Stuart)
- [ ] More work on io guide
- [ ] Spell check, all eyes on please!
- [x] Try and remove database warnings and add that undo function. 

A compiled version of the docs can be found here: http://sunpy.readthedocs.org/en/documentation_sprint/index.html

Any PR's to the documentation_sprint branch will be added on here upon merge.

Also:

*I HAVE REBASED THIS BRANCH, PULL FIRST!!*