swift234

Update generics proposal based on today's discussion. Major changes:
  - Use implicit conformance to protocols (duck typing)
  - Treat protocols as types, eliminating the any<proto1, proto2, ...>
  syntax in favor of... 
  - Introduce a syntax for anonymous protocols
  - Switch [] syntax over to be more C++-like
  - Switch protocol inheritance -> protocol refinement, and use : to
  separate a protocol from those protocols it refines
  - Clarify our intent w.r.t. type argument deduction
  - Note that we don't intend to implement run-time overload
  resolution out of the box



Swift SVN r497