DOC more complete coverage of API linking in examples

Previously ignored non-plot files.

Avoids some link over/undergeneration
TST add test for name identification in RST generation
TST avoid nose running setup() in gen_rst.py
TST add sphinxext to testing
TST remove dependencies for testing sphinxext
DOC remove HMM documentation
Merge pull request #3280 from larsmans/remove-hmm-docs

[MRG] remove HMM documentation
DOC fix versions of requirements in README.rst
Sparse input support in BaggingClassfier and BaggingRegressor #3241
Sparse support in Bagging #3241
Merge pull request #3286 from ilam/seconddoc

Sparse input support in BaggingClassfier and BaggingRegressor #3241
ENH fix astype usage to prevent copying

Removed where possible; using copy=False (from utils.fixes) where needed.

Also some C integer type fixes to gradient boosting.
DOC big fat warning about multithreaded BLAS
DOC correct bagging docs regarding sparse inputs
FIX RidgeClassifierCV didn't have scoring parameter

... but is advertised as having one
DOC typo in ExtraTrees
DOC add the Random Kitchen Sink synonym to the RBFSampler section

This should make it easier for people to find this code if they search for the
terms 'random kitchen sink' and 'python'.
Merge pull request #3297 from esc/doc/random_kitchen_sink

DOC add the Random Kitchen Sink synonym to the RBFSampler section
MAINT reduce amount of boiler code using standard C operations
DOC give example of binarizing binary targets

H/T @ilam