MAINT warn of future behaviour change proposed in #2610
DOC: move mean_shift docs to MeanShift

The class is linked from the clustering docs, while the function
isn't. Also standardized the spelling on "mean shift". StudlyCaps
version is an artifact of PEP8 class naming.
Merge pull request #2952 from jnothman/future_warn_two_labels

MAINT warn of future behaviour change proposed in #2610
ENH factor out squared norm helper
Now capable of treating sample_weights in feature space
FIX: Set correct impurity values in BestFirstBuilder
PEP8
Merge pull request #3049 from glouppe/tree-bestfirst

[MRG+1] Trees: set correct impurity values in BestFirstBuilder
target is response, not explanatory
typo: "fot" -> "for"
Merge pull request #3055 from ajschumacher/patch-3

typo: "fot" -> "for"
Merge pull request #3053 from ajschumacher/patch-1

target is response, not explanatory
FIX: weight impurity improvement by the size of the node
DOC: better doc for impurity_improvement
ENH: declare weighted_n_samples
ENH: rename Node attributes to avoid confusion
ENH: rename normalizer -> weighted_n_samples
ENH: renamed things too fast...
ENH: better API for passing weighted_n_samples
typo: "requiered" -> "required"