Enum docstring is hard to parse

[mdickinson]

The Enum docstring would benefit from a couple of examples showing common ways to use it. With the existing description it's rather hard to parse.

[mdickinson]

This would also be a good opportunity to pin down recommendations for use of Enum. E.g., I'd like to recommend that people always use an actual collection for the set of values, rather than using the Enum('MA', 'ME', 'MI') form.