add more WCS convenience methods: pixel_scale, celestial
fix headers in tests and a few other minor fixes; add changelog entry
fix bugs and add appropriate tests
allow for rotation in CD
remove emphasis in docstring (trying to fix sphinx warning)
address @astrofrog's comments by adding a warning and changing to a
method, but this commit leads to failures because of the filled cd
matrix + matrix math...
pixscale test fixes (logic fix, + more tests)
added a warning test, but it doesn't work!
fixed warning check
PEP8 and CHANGES fixes
rename get_pixel_scale -> get_celestial_scale
get_celestial_scale -> celestial_scale in utils
add pixel matrix property
use pixel_scale_matrix in celestial_scale util
another typo fix
return a qty
allclose instead of !=
add is_celestial and has_celestial and split out celestial/noncelestial
pixel scales
fix pixel matrix and imports
add units to pixel scale