Add python_requires in setup
With pip >= 9, this will ensure to install for a supported python version.
Like: >=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*
With pip >= 9, this will ensure to install for a supported python version.
Like: >=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*