Finish kitecore instruction set, compile to it

[hmac]

The kitecore VM language needs a few things in order to be a target for Kite compilation. Off the top of my head:

• handle default branches in case expressions
• handle foreign calls
• handle records

Once this is done, we can compile Kite to kitecore. We should then be able to pass kitecore straight to the VM and it should execute it.