clickable list brackets in type signatures

[ceedubs]

If you click on a [ or ] list brace in an implementation or doc example, it takes you to the doc for the List type; that's a really nice touch!

But a [ or ] in a type signature doesn't get the same treatment. For example in the type signature for Stream.toList it would be nice if I could click on either of the braces in [a].

[hojberg]

Hmm this looks to be a bit of a deeper issue than would appear on the surface. In signatures, it looks like we're not pretty printing them as a reference at all, but as a delimiter char.

I think this would have to be changed in the pretty printer somehow. @aryairani any thoughts?