Allow CamelCase version of snake_dict_to_camel_dict
(currently only dromedaryCase is supported)
Add reversible option to camel_dict_to_snake_dict
Add tests for both of these options
* Make camel_to_snake work on capitalized plurals
`TargetGroupARNs` should become `target_group_arns`, not
`target_group_ar_ns`
Promote `camel_to_snake` to top layer function but prefix
it with an underscore.
Add tests for improved `_camel_to_snake` function.
Reduce use of `re.compile` as it makes no sense when the
compilation result is not reused.
* Remove unused LooseVersion check
* Fix PLURALs case for camel_to_snake
Also renamed EXPECTED_CAMELIZATION to EXPECTED_SNAKIFICATION
