labelled traces

[waalge]

Following #838

Compact is nice. Could we have ?

trace(code, msg) 

I inline specs into validators as traces.
Be quite nice DX to have verbose printing of errors for humans, and then use codes when testing malformed txs.
atm its bit of a "goto" with line numbers.

// my_validator.ak 
trace (1010012, "Own Inputs are empty") 

// my_evil_test.ts
...
tx.collectFrom(ownInputs) 
...

try {
 tx.submit()
 } catch(err) {
  if (err.code == 1010012) {
    return true
  } else {
   throw Error(err)
   }

}

ad-libbing a bit here