Use try_files in Nginx config to serve docs.

Should handle /en/latest/ URLs, as well as single_version URLs.
Create single_version symlink.
Add nginx-smoke-test.py.

Run this test script to verify that a change to
the Nginx configuration behaves correctly.
Include pandoc. Refs #579
Specify pip version
Fix canonical page logic for single page sites
Single version*
Merge pull request #600 from rtfd/issue-293-part-two

Issue 293 part two
Fix canonical page variable placement
Use unicode string for format. Fixes #568.
Fix tasks logger too
Use https github links. Fixes #539.
Fix canonical url for htmldir. Refs #556
Missed a slash.
It's a boolean not a string :)
Sanitize canonical_url in template output
Don't return anything if its empty :)
Handle urls without scheme.
Add tests for canonical cleaning.
Add basic canonical URL docs