Method checkPreamble

Finds the next nonblank line, then trims the line and checks the preamble. Returns a DecodeReturn on the line if successful, else posts a fatal error. Sets the DecodeReturn's line number. The DecodeReturn has not yet been decoded. You'll need to do that with Code.decode(...)

(String preamble, final EvolutionState state, 
        final LineNumberReader reader)