Refs #25 - Removed virtualenv creation from Makefile. Added documentation about typical development environment setup and usage.
Refs #25 - Removed reference to docs/_static (does not exist) in Sphinx configuration.
Refs #25 - Moved contributor's guide to CONTRIBUTING.rst file.
Refs #25 - Fixed wrong reference to 'contributing' in documentation.
Merge pull request #26 from python-hospital/25-no-virtualenv

Removed virtualenv creation from Makefile. Closes #25.