Update installation.rst

Fix a few typos and make a clear distinction between installation and configuration steps.
Add a test runner
Add some more tests to validate customer linking
Fix single-quotes
Add travis integration
Fix readme formatting
Fix readme formatting
Fix Travis CI image
Fix travis config
PEP8 Fixes
Drop support for 2.6
Drop Python 3 targets for now

There seems to be something about the packaging/setup
that breaks in Python 3 environments.
Update Travis Image
Add test to exercise webhook
Switch to request.body for Django 1.5 compatibility

Thanks, Fred Palmer (https://github.com/fredpalmer),
for the patch.
Fix deprecation warning re: urls.defaults

Thanks, Fred Palmer (https://github.com/fredpalmer)
Merge pull request #24 from eikonomega/master

Installation Doc Update
Add mock to the list of requirements for tests
Properly case the settings.py reference
Add Checkout.js example