Add license information to setup.py

[cchang5]

I wanted to help add licensing information in setup.py as follows.

    license="MIT",
    classifiers=[
        "Intended Audience :: Developers",
        "Programming Language :: Python",
        "Environment :: Web Environment",
        "Framework :: Flask",
        "License :: OSI Approved :: MIT License",
        "Programming Language :: Python :: 3",
        "Programming Language :: Python :: 3.5",
        "Programming Language :: Python :: 3.6",
        "Programming Language :: Python :: 3.7",
        "Programming Language :: Python :: 3 :: Only",
    ],

It would help automatically parse for the license of this library. Thank you.

[gmacon]

I would happily merge a PR with this change.