remove overview

doc/source/overview/brain.rst

doc/source/overview/comparing.rst

doc/source/overview/database.rst

doc/source/overview/examples/Cam_blender.svg

doc/source/overview/examples/Python_blender.svg

doc/source/overview/examples/apcv.py

doc/source/overview/examples/asv_brain.py

doc/source/overview/examples/contrast_weighted_nearness.py

doc/source/overview/examples/get_posorients.py

doc/source/overview/examples/load_image_posorient.py

doc/source/overview/examples/load_image_rowid.py

doc/source/overview/examples/michelson_contrast.py

doc/source/overview/examples/pcv.py

doc/source/overview/examples/ridf.py

doc/source/overview/examples/scene.py

doc/source/overview/examples/skyline.py

doc/source/overview/examples/static_brain.py

doc/source/overview/index.rst

doc/source/overview/moving.rst

doc/source/overview/processing.rst