Printed model

[arthurpaulino]

We want to automagically maintain two files for specification and inspection purposes:

• model.dbg, which is the raw debug output of our model
• model.lem, which is a more readable version of it, using our macro syntax

There should an example that prints those files. Something like cargo run --example print_model

There should also be a test asserting that those files match the output of the most updated printing. If not, the test should suggest running the printing example.