Prepare for OCaml interpretation

Signed-off-by: Christoph Höger <christoph.hoeger@tu-berlin.de>
Add an ocaml interpreter to the dynamics

This allows for evaluation of embedded OCaml expressions. Unfortunately
for true fidelity (e.g. lambda-arguments to OCaml functions), we'll
need the mcl2ocaml compiler in place.

We also need an "Unhost" expression for unpacking the OCaml values back to
mcl.

Signed-off-by: Christoph Höger <christoph.hoeger@tu-berlin.de>