new CubeList method to extract over common coord values
Changed to generator comprehension
Default NetCDF dimensionless unit.
Simplify circularity test in nc load rules.
Define circularity from bounds, if any.
Added tests for old+new circular logic.
Fixed aggregate_by bug for single values coordinates.
Prevent a copy from having writable coordinate values on a DimCoord.
Updated the what's new. Better, but not complete.
Isolate pandas plotting side-effects.
Merge pull request #1210 from rhattersley/pandas-side-effect

Isolate pandas plotting side-effects.
What's new changes.
Merge pull request #20 from bjlittle/whats_new_actions

What's new changes.
Merge pull request #1212 from pelson/whats_new_review

Updated the what's new. Better, but not complete.
fixed bug when comparing string fill values
Merge pull request #1208 from pelson/aggregate_by_small

Fixed aggregate_by bug for single values coordinates.
Updated default mdtol for AreaWeighted.
Merge pull request #1214 from esc24/isnan_string_bug

fixed bug when comparing string fill values
Merge pull request #1215 from pelson/area_weighted

Updated default mdtol for AreaWeighted.
Extend test to cover bounds case.