Remove python2.6 from
- Travis
- Tox
- PyPi tags
- documentation and readme

Also, Simplify an import clause.

This fixes #133

- Adds link to the user guide from readme
- Adds a new page to the user guide on "working with files"

Add OAuth and update docs

- Remove :ref:s from the headers, since they made the latex build crash
- Add logo

Remaining issue:

- Can't get headings levels right on both the html and the latex builds
  at the same time. More info in #40