minimum setuptools version

[carlwgeorge]

Currently the setup.py file is using environment markers to define the colorama and enum34 dependencies. Those are only present in setuptools 20.6.8 or newer. There are a two ways we can handle this (I can do an appropriate pull request once I know which one you prefer).

1. Remove the environment marks and dynamically generate the requirements list.

requirements = []
if platform.system == 'Windows':
    requirements.append('colorama')
if sys.version_info[:2] < (3, 4):
    requirements.append('enum34')

    install_requires=requirements,

2. Document the minimum setuptools version needed in the setup_requires parameter of the setup function.

    setup_requires=['setuptools>=20.6.8'],

[laike9m]

I'll go with the second approach.