get_many and set_many should work the same way as in other cache backends

Instead of raising an exception it should just return without doing anything.

Instead of raising an exception it should return an empty dict

This is the same behaviour that the default Django cache backends have.

Bugfix: set_many does not set key version

Use line blocks to preserve AUTHORS formatting.

Use line blocks to make sure that each entry in AUTHORS.rst appears on
its own line, as opposed to squished up in one paragraph.

Jf/delete many

RedisDummyCache

Clean up get_or_set.

Update import of importlib

Work around `RemovedInDjango19Warning`. Fixes #93

Docs