Rfcs: Syntax sugar for prefix-style type parameter lists.

[rust-highfive]

This is a proposal for type parameter lists that come well before the
actual generic items. Example:

type <T: Unwieldy+Traits+Go+Here,
      U: Even+More+Traits> {
  fn foo(t: T) -> U { ... }
  fn bar(u: U) -> T { ... }
}

Tracking issue for postponed PR #122

[nrc]

Where clauses have been pretty successful, and so I don't think there is quite the motivation for this feature any more. I propose we close this issue, any objections?

[Centril]

After Nick's triage two years ago there has been zero movement and I don't think this is going anywhere; so I'm closing this.