ENH: fixing pyflakes / pep8, trying to improve readability
ENH: addressing discussion
ENH: consistency for quation marks
ENH: missing commit
ENH: ... a few more missing quotation marks.
FIX: adding back directives
ENH: notes on examples
ENH: misc
- adding directives where missing
- fixing categorial interaction plots example
- improving example.rst
Merge pull request #652 from dengemann/fix_pep8_doc

WIP: fixing pyflakes / pep8  closes #644 closes #645