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
Merge branch 'minimal_mask_implementation' of git://github.com/keflavich/spectral-cube into minimal_mask_implementation
WCS tests
added docstrings, dropped dropdeg from io
Sanitize orientation of 3+1 cubes
Merge pull request #3 from keflavich/minimal_mask_implementation

added include/exclude properties on mask, implement data_valid
Merge pull request #6 from ChrisBeaumont/orient

Propertly Orient PPV+single stokes data
Implemented initial spectral_axis and spectral_slab
Improvements to slab code