ENH: output processing speed in MB/s for vectorizer example

Moving common text feature extraction methods in a new base class

Hashing vectorizer work in progress
Initial work on hashing vectorizer
Add fit_transform support using the TransformerMixin + missing ABCMeta marker
Improved the clustering example with HashingVectorizer
Remove TransformerMixin from vectorizers and do a direct fit_transform alias for HashingVectorizer instead
Improve module docstring of document clustering example
COSMIT make BaseVectorizer a mixin
cosmit
Merge branch 'master' into hashing-text-vectorizer
Updated whats_new.rst
DOC: Started section on hashing vectorizer in narrative section
Merge branch 'hashing-text-vectorizer' of git://github.com/ogrisel/scikit-learn into clustdocs