ENH Rewrote CountVectorizer fit_transform to be ~40% faster

Performance Results: http://i.imgur.com/5IGEz3Q.png
fix numbering for tutorials page
DOC PR means pull request

In response to #1882.
FIX BytesIO and urllib usage in fetch_olivetti_faces

Fixes #1872.
Update hmm.rst

Should use model2.predict(X) instead of model.predict(X).  The predicted states, though, will have a different sort order than the generating model.
Add bit more instruction on writing docs
big O/tilde add in
removed old complexity info
DOC: remove typo
FIX gen_rst.py was something using an undefined variable
Merge pull request #1886 from NelleV/DOX_fix

FIX gen_rst.py was something using an undefined variable
ENH refactor and further speed up CountVectorizer
DOC I didn't mean soft-O by "tilde notation"
DOC: libatlas3-base in requirement

See discussion in issue #1877
Release GIL around sparse liblinear training
TYPO fix
ridge regression uses compute_class_weight()
Re-add deprecated class_weight parameter.

Now it is present in both RidgeClassifier.fit() and
RidgeClassifierCV.fit() for consistency, and it is actually used.
removed class_weight parameter from RidgeClassifier.fit()
stochastic_gradient: fix mistake in _init_t docstring