Execution time of mapping generation is now displayed.

Initial testing using rt.jar (most of the Java standard library - a 60MB file)
with the ASM Jar files is showing around a 200ms execution time increase per
regular expression. I expect this increase to be almost linear considering
each RegEx must pass over the entire method digest.

Future work: consider separating the work out into multiple threads. Once
created, the method digest is immutable and can be shared between threads.