Fix documentation not building because of docstrings style

MR to fix the issue #1300.

Adding Napoleon extension to sphinx. With the new extensions, some other errors came up.

The funtions that have the decorator @taurus4_deprecation(alt=".warnings[1]") needed to have a mandatory docstring. Some of them already had "for backwards compat with taurus < 4", so I added it to the remaining functions that did not have it. Anyway, when checking the docs in the web these do not appear. I think they were simply warnings treated as errors because of the -W argument in sphinx-build.