DOC: silence several Sphinx warnings when building the docs

Fixes some twenty-odd Sphinx errors/warnings, mostly typos, unshielded markup (*, | etc), and complaints about duplicate references. The latter seem to be related to the fact that numpydoc mangles the numeric references, but not abbreviations, so that eg `[1]_` gets a unique number, but `[CT]_` does not.

No attempt is made at `document not included in any toctree` warnings of https://github.com/scipy/scipy/pull/3893

Done with @dimazest and @itziakos during the Bloomberg hackathon last Sunday.
@dimazest you have more fixes in your fork, correct?
 


A double underscore creates an anonimous target http://docutils.sourceforge.net/docs/ref/rst/restructuredtext.html#hyperlink-targets

The issue here is that there are two references which start with `here <url>`  with different URLs (the other one in the second paragraph of the Notes section). Unless at least one of them is anonymous, Sphinx gets confused.