[HORN] Protect names of stateless nodes with a _fun suffix. This was conflicting with existing names in Z3, ie. "abs".
[HORN] Better treatment of stateless nodes collecting semantics
       Fixes issue #13 on github: https://github.com/coco-team/lustrec/issues/13

Renamed ISet of Machine_code to VSet: was sets of variable and was conflicting with ISet from Utils which carries strings.

This is used in EMF backend.

const that are not dimension types should not be used to evaluate dimension expression. This happened with const variables denoting real values.

- EMF backend now impose the optimization level to be set to 0 in order to avoid equation elimination that would render traceability difficult
- Options.ml has been split into Options.ml / Options_management.ml. Options.ml only contains references and no functions

- Addtional encapsulation of machine_code instr in a struct to enable future extension of type with more metadata.
- Improved EMF backend with META information

[bug] seems to crash with EMF backend