use the .data parameter when imshowing pv_slice
Added BSD License
Make spectral_cube an optional dependency
Merge pull request #28 from ChrisBeaumont/master

Add license
Merge pull request #34 from ChrisBeaumont/deps

Make spectral_cube an optional dependency
Typo -- wrong exception type
Merge pull request #35 from ChrisBeaumont/deps

Fixes a typo in #34.
another typo
Merge pull request #37 from ChrisBeaumont/deps

Another typo
Merge pull request #32 from keflavich/minorfix_issue32

Conversion to float error?