Introduce getRegex() method on a Symbol.

It concats regexes from extended fields and returns it

Change-Id: I46c3cfb5c9c2d0e4b6073bffbcac8e6428499a88
Show symbol's name in debug message of grammar inference.

Change-Id: I892f8b24a6c4253a19dec962711bfdb44834c20b
Fix an error in the generation of mutations of BinaryType.

A string cannot be edited like an array.

Change-Id: Ib058fb97bfadb6c32b427ad3d3da75f7b20022ad