P3K: Changed StringIO to BytesIO to fix a failing test.
Merge pull request #1279 from amueller/one_hot_encoder

MRG added OneHotEncoder
FIX don't use pl.subplots.
ENH adding "apply" to random forests
ENH add RandomHashingForest estimator.
ENH added docs, example and tests.
DOC Some narrative documentation for Random Forest Hashing.
FIX for sparse matrix in RandomForestHasher
ENH refactor inheritance structure.
ENH use random regression task to avoid memory overhead of n_sample classes.
Modifying cython for tree building would still be better... (via new criterion?)
ENH Added Example
DOC added references
MISC renamed RandomForestHasher to RandomForestEmbedding
MISC don't use pl.subplots, fix typo
MISC rename plot_random_forest_hasher to plot_random_forest_embedding
ENH fix plot in docs. thanks @ppret.
DOC forgotten rename
DOC fixed links in whatsnew.
DOC added dump_svmlight_file to the references
DOC improve MinMaxScaler narrative docs.