Issue 9695 - Emit enum member initializer in ddoc.

http://d.puremagic.com/issues/show_bug.cgi?id=9695

Only user-specified inititalizers are emitted, but this can be changed. The reason why is I wanted to avoid emitting initializers for members where the initializer isn't important:

```D
enum Wheelies
{
    car, bike, bicycle
}
```