Removes setup import from distutils that overrides setuptools setup.
Tidies up Python 2.6 dependencies

Moves all dependencies to the install_requires argument to setup.
Updates PyPI trove classifiers.
Merge pull request #158 from gotgenes/bugfix-dont_override_setuptools_setup

Improve packaging configuration.
Use requirements files to consolidate dependencies.
Merge pull request #159 from gotgenes/feature-use_requirements_files

Use requirements files to consolidate dependencies.