add 'save' to quicklooks
with_mask checks for broadcastable, not equal shape
clean up tests of broadcastability
Merge pull request #166 from keflavich/quicklook_save

Minor fixes: quicklooks, with_mask test
bugfix: with_mask should be usable when no `_mask` is defined
Merge pull request #172 from keflavich/with_mask_no__mask

bugfix: with_mask should be usable when no `_mask` is defined
update apt-get listings (fixes graphviz install issue)
add to_ds9 feature
fix to_ds9 docstring sphixn warning