lang: Add jumps (tail calls) ...

This isn't the cleanest implementation but it works.

lang: Add more code documentation

lang: Always place VmState first in function calls

lang: Remove arg_count and rely on stack depth instead

lang: Add opaque types for Object and VmState

lang: Handle vm_state creation in vm

lang: Add back reference counting ...

The basic idea here is that we transfer ownership to and form the stack,
and clean up references that way.

vm: Add stack pushing and popping

lang: Rename vm.stack to vm.stack_next

lang: Add stack bases to vm

lang: Wrap stack functions

lang: Replace args with a vm_state stack ...

This doesn't have any functional changes at the moment but will
aid in adding proper stack support in the future.