NMT: Implement Hagelbarger Code

This will correct burst errors of received messages. If the message
is too corrupted, it will be ignored, because some element may not
match then. The digits and line signals are checked for consistency,
since they are repeated serveral times in a message.

.gitignore

@@ -35,3 +35,4 @@ src/test/test_emphasis
 src/test/test_dms
 src/test/test_sms
 src/test/test_performance
+src/test/test_hagelbarger