allow user actions in debug mode

[chdelfosse]

I suggest to add a one line mod (actually addition) "lexobj.lexdebug=debug" at line 980 of lex.py

in order to allow a line ( in a lex user rule) if t.lexer.lexdebug: print("beginning %s"%t.lexer.FUTURE)

the functional code would NOT be impacted the suggested element begins with 'lex'