add GBRT to covertype benchmark
WIP: remove asserts
WIP: use C-based random number generator
WIP: set n_classes as ndarray
FIX: fix test_random_hasher
WIP: fix adaboost
WIP: small optim to regression criterion
WIP: optimize tree construction procedure
WIP: optimization of the tree construction procedure
cleanup
recompile _tree.pyx
FIX: export_graphviz test
FIX: set random_state in adaboost
FIX: doctests
FIX: doctests in partial_dependence
FIX: feature_selection doctest
FIX: feature_selection doctest (bis)
WIP: allow Splitter objects to be passed in constructors
FIX
Some PEP8 / Flake8