MRG: Fix FeatureAgglomeration docs
FIX: Raise AttributeError for fit_predict
Replace feature with sample
Merge pull request #3946 from MechCoder/doc_fix

[MRG+1] Fix FeatureAgglomeration docs
FIX bug in fit_params assumed to be an array

Fixes gh-3957.
DOC: make LinearSVR appear in the doc reference
DOC fix/expand Imputer example docs

Fixed formatting of Script output in text introduction.

Added more details to the introduction on use cases for imputing.

Fixes gh-3918.
ENH FIX Raise ValueError when the target does not match with classes arg

ENH Use np.searchsorted to find the index instead of cls2idx
TST Added NRT to test if ValueError is raised during target mismatch.

This test will be removed when a more general test is added.