ENH: Get version to update appropriately in PDF and HTML

[fletchapin]

Use Case

On the title page of the PDF or header of the HTML documentation there is a version listed, and right now it always defaults to version EXPERIMENTAL.

Solution

The version is defined here in conf.py. The os.getenv call should be fixed to figure out the version in a different way since Travis is no longer being used, TRAVIS_TAG is undefined.

Alternatives

The version isn't super important so letting it default to EXPERIMENTAL is probably fine.