[Yhc] Yhc.Core format changes

Hi all, especially Dimitry, I've had to change the Yhc.Core format, sadly, so all Yhc.Core users will need to: 1) Pull a fresh copy 2) Clear their inst/lib/*.yca files 3) Rebuild yhc The change is minor, but important. This introduces a new form for the Core language, Lambda expressions. They are never used in the generated code by Yhc, and most transformations can successfully ignore them, but certain things require them, and when they do, there is pretty much no way around it. The extra constructor added is: CoreLam [String] CoreExpr Which has identical meaning to the Haskell construct: \arg1 arg2 -> expression Sorry for doing this, I really hope to never break the Core format again. Thanks Neil