Scan syntax tree for procedure calls

[Araq]

The enum solution indicates that you can do things like:
    
    
    proc flexibleButPointless(m: Mode) =
      with db, m:
        t["foo"] = bar
    
    
    
    Run

which never come up in reality, but the macro needs to protect against. It's 
only a `static` keyword away though so it's not too bad.