Rename features --> feature_extraction to match module feature_selection.

scikits/learn/__init__.py

scikits/learn/datasets/mlcomp.py

scikits/learn/feature_extraction/__init__.py

scikits/learn/feature_extraction/image.py

scikits/learn/feature_extraction/tests/__init__.py

scikits/learn/feature_extraction/tests/test_image.py

scikits/learn/feature_extraction/tests/test_text.py

scikits/learn/feature_extraction/text.py

scikits/learn/setup.py