added include/exclude properties on mask, implement data_valid
add WCS dropdegenerate tool
degeneracy dropping, minimal data indexing
two more manipulation routines
swapaxes used in spectral_cube now
drop degenerate in WCS too
shape returns _data.shape
WCS tests
added docstrings, dropped dropdeg from io
Sanitize orientation of 3+1 cubes
refactor orientation
Merge branch 'master' of github.com:radio-tools/spectral-cube

Conflicts:
	spectral_cube.py
	test_spectral_cube.py