Merge branch 'enh/bitmap' into 'master'

CHANGELOG.rst

README.rst

doc/fsl.data.bitmap.rst

doc/fsl.data.rst

fsl/data/bitmap.py

fsl/data/gifti.py

fsl/data/image.py

fsl/data/imagewrapper.py

fsl/data/utils.py

fsl/utils/naninfrange.py

fsl/version.py

requirements-extra.txt

setup.cfg

tests/test_bitmap.py

tests/test_gifti.py

tests/test_image.py

tests/test_imagewrapper.py

tests/test_naninfrange.py