Fixing Sphinx warnings and preventing more from occurring.

Removes 4 warnings from Sphinx about non-anonymous hyperlinks and adds flag to prevent ill-formed restructured text from being checked-in.

We can think of the `-W` flag as a sort of "will it compile into actual docs" flag for `sphinx-build`.

This will prevent future docs maintenance commits such as 6dd5f2b308169ff61b51bf3f4f3a2b768d6f9127 and those in PR #206