Make test requirements install normal requirements

This requires implementing the pip recursive requirements feature
in setup.py.
Fix README so that the example code runs
Indent and syntax highlight README code snippets
Add pip details to the top of the README
Merge pull request #15 from alphagov/bugfix-readme

Improve requirements installation and README
Add coverage and refactor test execution

- Use nosetests task rather than test as test support is deprecated,
  see;
  https://code.google.com/p/python-nose/issues/detail?id=219&can=1&q=with-doctest%20python%20setup.py%20test&colspec=ID%20Type%20Status%20Priority%20Stars%20Milestone%20Owner%20Summary
- Move nosetests flags into setup.cfg as per the docs, see;
  http://nose.readthedocs.org/en/latest/api/commands.html#nosetests-setuptools-command
- Switch on coverage and xunit output
Add coveralls support to travis build