Allow for alternatives to 'GENERATED CODE' to indicate generated files

[mitchgrout]

It would be convenient to be able to use a different phrase, rather than "GENERATED CODE". Possibly this could involve accepting one (or more) options from the command line, like

$ lizard --generated-comment MY_GENERATED_CODE_COMMENT path/
$ lizard  -g                 MY_GENERATED_CODE_COMMENT path/

...with the default value being "GENERATED CODE". I'd be happy to implement.