Move enum initializer to be before enumeration cases

[sindresorhus]

In the HTML output.

I have an enum with a lot of cases and the user has to scroll all the way to the bottom to see the initializer, which I would argue is more important.

[mattt]

@sindresorhus Thanks for your feedback on this. This is a detail that I've gone back and forth on.

The challenge is that enumerations can be used in a few different ways, each prioritizing different information. For example, cases are more important for RawRepresentable enumerations, whereas initializers are more important at other times.

...actually, thinking about this again in relation to a solution proposed for #101:

Organize the symbol into a group with others for that protocol that are separate from type-specific declarations.

That would address the RawRepresentable case that motivated the current ordering. Given that, I agree — let's switch up the ordering. I can get a PR for that within the hour.

Edit: Ready for review: #103