Commit some incremental progress on the K3 AST

Commit some incremental progress on the K3 AST

This snapshots some crude attempts at getting generic tuples
into the K3 AST.  At the moment it isn't working (for somewhat
annoying reasons involving universal quantification, I think)
and the AST is wired up to have tuples 2-4 (though more are
a simple matter of copy-paste-modify in a few places); some bits
are automated, but many aren't.