Fix error in write
Change clobber -> overwrite in write
Small improvements to docs
Preserved requested spectral unit
Tidy up initialization of new cubes from modified version of existing cubes.
Set _spectral_unit only in with_spectral_unit
Minor fix
Pass new meta
Fix propagation of spectral unit
Merge pull request #92 from astrofrog/improve-toc

Small improvements to docs
Check that WCS auto-changes unit and that spectral_unit is needed
Merge pull request #91 from astrofrog/preserve-spectral-unit

Preserve spectral unit requested
Merge pull request #86 from astrofrog/misc-fixes

Misc fixes