MAINT: Slight refactor.

Moves numpy version determination out of the loop which was causing a
significant impact on performance due to namedtuple class construction.
Switch to simultaneous conda install.
Merge pull request #1335 from cpelley/regrid_refactor

MAINT: Slight refactor.
Proposed fix for #1167.

Fixes saving cubes with reserved attribute names to netCDF.
Added test for saving cube to netcdf with clashing reserved attribute.
Use array's copy method instead of copy.copy().
Merge pull request #1336 from ajdawson/cube-copy-mask-maint

Use array's copy method instead of copy.copy().
Use getncattr when loading global attributes.

Avoid a situation where an attribute whose name clashes with a
netCDF4.Dataset attribute (e.g., dimensions) will end up with the
value of the netCDF4.Dataset attribute instead of the actual
attribute from the netCDF file.
Add a package init file for the cf tests.

Otherwise the tests aren't run!
Fix support for descending coordinate order.
Merge pull request #1326 from ajdawson/setncattr

Fix for netCDF4 reserved attribute names.
Merge pull request #1349 from rhattersley/concat-fix

Fix concatenate for descending coordinate order.