Added:
- Fixpoint operator (it heavily relies on the type safety/progress
proofs, so those get more priority from now)
- Stop (so that I can kill a process if necessary. Though this can be
achieved in other hacky ways (many case expressions
- the two types of live expressions: computations and expressions
  A computation is a placeholder for an actual OCaml () -> () function
which will be the primary way of code execution
  An expression is just a regular expression and behaves as such

Fixed: The missing inl, inr markers on return from a fork (otherwise the
case expression makes no sense)