* fix the issue with max_depth and BestFirstTreeBuilder
* fix the test
* fix max_depth overshoot in BFS expansion
* fix forest tests
* remove the warning, add whats_new entry
* remove extra line
* add affected classes to changed classes
* add other affected estimators to the whats_new changed models
* shorten whats_new changed models entry
* FIX MAE reg. criterion: Use safe_realloc to avoid memory leak
* Release GIL in safe_realloc and clean up scaffolding
* As gil is released in safe_realloc, no need of a with gil block
* Use except * to propagate error in all cdef functions
* Don't use except * for functions that return python objects
* Don't use except * for the comparison function passed to qsort
* Omissions and Errors
* Use safe_realloc now that gil is released there
* Fix realloc size
* Acquire GIL only if we need to raise
* Use except * more judiciously; Release gil only when raising; Add comments to clarify
* Actually that was unneeded; realloc will also allocate for the first time
* StackRecord*, PriorityHeapRecord* to fused type realloc_ptr; Use safe_realloc
* Use except -1 to propagate exceptions. This should avoid overheads
* Fix docstrings and add return 0 to reset methods
* TYPO
* REVIEW Remove redundant MemoryError raising calls
* remove unused condition in decision tree construction
* edit is_leaf condition for min_weight_leaf
* edit ordering of statements
* remove extra parens and add whats new
* feature: add beta-threshold early stopping for decision tree growth
* check if value of beta is greater than or equal to 0
* test if default value of beta is 0 and edit input validation error message
* feature: separately validate beta for reg. and clf., and add tests for it
* feature: add beta to forest-based ensemble methods
* feature: add separate condition to determine that beta is float
* feature: add beta to gradient boosting estimators
* rename parameter to min_impurity_split, edit input validation and associated tests
* chore: fix spacing in forest and force recompilation of grad boosting extension
* remove trivial comment in grad boost and add whats new
* edit wording in test comment / rebuild
* rename constant with the same name as our parameter
* edit line length for what's new
* remove constant and set min_impurity_split to 1e-7 by default
* fix docstrings for new default
* fix defaults in gradientboosting and forest classes
Adrin Jalali