Make SpectralCube stokes-agnostic
Moved orient utilities to cube_utils
Make FITS loader deal with 3- and 4-d data
Fix 4-d cube reading
Fix WCS re-ordering
Fix FITS writing
Added TODO
Address comments by @keflavich
Merge pull request #17 from astrofrog/stokes-refactor

Stokes refactor
minor change
implemented 9ish actions
application along arbitrary axis
implementation of flattened slices
fixes to spectral cube definition
repr
add slices
add repr for cube
remove __getitem__ - it is problematic
slice mask appropriately in flatten
same as previous commit, just propagated further