Moved all curnel code into curnel/, and split the two kernel modules
into separate files. Now the trusted core and the module/#lang stuff are
in separate files. The #lang is now reprovided by "cur.rkt", which
should also provide core agnostic sugar.
* Removed auto currying from core. These are now provided by sugar.
* Exposed type-infer, type-check, and normalize
* Attempting to track down strange bugs regarding local-expand
* sigma, gamma extended at expand time
* All type-checking happens at expand time
* Locally expand all forms into core redex forms. However, this seems to
be causing problems. Probably not controlling expansion just right.
* STLC + syntax for writing STLC terms naturally, without explicitly
applying inductive constructors.
* Complete STLC type system, although it's not quite correct yet.
