Update the docs to maintain compatibility with the latest version of sphinx.

[rsyi]

This addresses the following issue: #27

I converted all the markdown files to .rst files. Because the readthedocs currently read from my repository (rsyi/pylift), this merge is not critical, and the docs have already been updated (if there is an official RTD wayfair account, I'd be happy to add it as a maintainer).

Some other small changes:

• Centered the image in the "Introduction to Uplift" section.
• Updated the copyright year.
• Advanced the version to the current version (0.1.0).
• Adjusted setup.py to have requirements (for pypi).
• Re-ran sphinx-autobuild with the most recent version of sphinx, to ensure future compatibility.
• Added some additional documentation regarding the ability to pass a tuple instead of a dataframe to TransformedOutcome, pypi installation support, and the possibility of using a continuous outcome.