Tox and travis for Django 1.3, 1.4 and 1.5

* Add tox config for Django 1.4 and 1.5. Django 1.3 tests are broken.
* Fix tests for Django 1.3.
* Don't hard code interpreter version in tox config.
* Update contributing docs to show how to run tox tests.
* Add Django 1.3 to travis builds.
* Add override settings dependency for Django 1.3 to travis builds.
* Add python 2.6 to tox config.
* Fix tox/travis so that they test the lastest release of each minor version.
* Add a note to contributing doc to install tox first and make example commands more consistant.
* Add note about backwards compatibility import.
Clean up the docs

* rework usage docs to make them easier to parse and show up in index
* move install to quickstart on front page
Merge pull request #24 from willkg/docs-tweaks

Clean up the docs
Drop 1.3, add 1.6, fix #25.
Drop django 1.3 from tox.ini
Fix version pinning in travis.
Add django 1.6 to tox.
Also add support for running tests against 3.3.
Use pypi releases for 1.4/1.5, github for 1.6rc1.
Missed a quote.
Merge pull request #28 from jasonkeene/travis-version-pinning

Fix version pinning in travis.
Merge pull request #29 from jasonkeene/tox-and-16

Add django 1.6 to tox.
Version 0.4.0
Tweak docs to cover reverse proxies better
Merge pull request #30 from willkg/tweak-ratelimit-docs

Tweak docs to cover reverse proxies better