ENH: support basinhopping solver in LikelihoodModel.fit()

- new _fit_mle_basinhopping()
- minimizer kwargs can be passed using 'minimizer' kwarg of dict type
DOC: clearer minimal example
DOC: review
DOC: minimal example text
minimial example formulas
DOC: min ex review
Merge pull request #927 from vincentarelbundock/minimal_example

DOC: clearer minimal example
base converged flag on res.message in _fit_mle_basinhopping()
use of score and hess arguments in _fit_mle_basinhopping()
update docstring of LikelihoodModel.fit()
TST: new TestProbitBasinhopping
add *args to _check_perfect_pred()
TST: remove no-op callback in TestProbitBasinhopping.setupClass()
Merge pull request #932 from rc/basinhopping

ENH: support basinhopping solver in LikelihoodModel.fit()
BUG fix lowess sort when nans closes #946
Merge pull request #949 from josef-pkt/fix_lowess_946

BUG fix lowess sort when nans closes #946
Another round of pyflakes/pylint cleanup. This commit covers the emplike and formula modules.
Fixed pyflakes in genmod: only one import error fixed due to overwrite in pull request 915.
Fix a docstring in KDEMultivariateConditional.
Merge pull request #956 from dougalsutherland/kde-doc

Fix a docstring in KDEMultivariateConditional.