move around examples for better structure.

doc/datasets/twenty_newsgroups.rst

doc/developers/performance.rst

doc/modules/clustering.rst

doc/modules/cross_validation.rst

doc/modules/decomposition.rst

doc/modules/feature_extraction.rst

doc/modules/feature_selection.rst

doc/modules/grid_search.rst

doc/modules/lda_qda.rst

doc/modules/learning_curve.rst

doc/modules/linear_model.rst

doc/modules/model_evaluation.rst

doc/modules/neural_networks.rst

doc/modules/pipeline.rst

doc/modules/sgd.rst

doc/tutorial/basic/tutorial.rst

doc/tutorial/text_analytics/working_with_text_data.rst

doc/whats_new.rst

examples/bicluster/README.txt

examples/classification/README.txt