Use some Python3 idioms.
Use print function instead of statement.
Use absolute imports.
Add __future__ division on files where it matters.

These are the files where the code expects integer division, and so
needs to explicitly ask for it when using __future__ division.
optimising
First vectorised rules -- only time coords for now.
Fixed problem with new test in tests/integration/test_pp.
reinstated scalar only _convert_scalar_time_coords() in pp_rules
reverted some test changes that are unnecessary now that alternative code path is not used
tidy up to test__convert_time_coords.py
Merge pull request #1387 from marqh/trans_optimise

optimising
translations
removed unnecesary array copies
readability
more use of np.asarray and other tidying
Merge pull request #1391 from marqh/uglitch

STASH->CF translation fixes
testing
additional tests
one more test
Add ConversionMetadata named tuple.