Add lifting of host values

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

the host expressions require parenthesis

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

Added a new operator (Client) to lift Ocaml values back to
mcl.

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