[Yhc] Yhc.Core format changes

[Neil Mitchell]

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