DOC: intro to formulas
Merge pull request #619 from vincentarelbundock/formula_example

DOC: intro to formulas
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
DOC: fix example_interactions.py (ipython directive reports indentation error with failure try except)
a typo in the doc strings of mcnemar in runs.py correction parameter continuity corection -> continuity correction
Merge pull request #663 from otterb/master

DOC: A typo in runs.py doc string for mcnemar test
BLD: protect open file
BUG: generic likelihood explicit None check
Maint: gitignore: add dist (./dist doesn't work)
BUG: add missing ``__init__.py`` to test folder, add helper script
BUG/DOC: fix refactoring victims in ex_regressionplots
TST: TestProbitCG: increase optimization precision, closes #109