wip on fx interactions for GBRT
Merge branch 'master' into gbrt-interactions
implemented partial dependecy plot
fix: grid and model
cleaned tree traversal and sorted out weighting
cythonized and cosmit
automatically create grid from training data
cosmit
docstrings
add cartesian product
partial dependency plot example from ESLII 10.14.1
Merge branch 'master' into gbrt-interactions

Conflicts:
	sklearn/ensemble/gradient_boosting.py
Merge branch 'master' into gbrt-interactions
Merge branch 'master' into gbrt-interactions
add learn rate to partial dependency function
common ylim; comment out 3d plot
make fit_stage private
return axes instead of grid
3d plot of 2-way interaction plot
Merge branch 'master' into gbrt-interactions
multi-class is supported
cosmit