Merge pull request #2201 from NelleV/MEP10_fixes

FIX small fixes in numpydoc's titles
Merge pull request #2200 from NelleV/PEP8_docstring

ENH docstring is now PEP8
DOC modified sphinx's layout.hml

The previous sphinx layout relied on overriding a default template.
It meant we could not easily add links and other things in the header.
The new layout does not inherit from anything, hence makes it easier
to tune.
DOC the space between titles and the rest is now bigger
DOC improved spacing between functions, classes and the rest