First step to have semantic rules into the data-model

This MR should bring

• a simple definition of semantics rule in the data-model
• an example of interpreter code generated for one instruction from its semantic rule

Review Hint:
The successive commit replace parts of the hard-coded body of CAR with generated ones. You can notice that there is no change in the generated file as thes generation match the hard-coded version (variables names in the semantic rule have been choosed for that purpose).