Add PartialDateTime
Merge pull request #885 from rhattersley/partial

Add PartialDateTime
Experimental regrid.
Unicode tests updated, new reference string files added
Merge pull request #873 from bjlittle/orca_to_atmos

Experimental regrid.
Review actions: comment added, sys module introduced now explicitly removed at contextmgr exit
Merge pull request #889 from dkillick/unicode_tests

Unicode tests improvements
Switch to biggus for deferred loading.
PPDataProxy exposes consistent dtype
Update tests.
Remove obsolete import.
Convert to Numpy/Ortho adapters
Update test
Revert test
Preserve old merge behaviour
Update test
Fix _create_field_data and tests
Fix tests for iris.fileformats.pp._interpret_fields
Fix indexing test result
Add support for fill_value