Made all debug output go through the 'debug_print()' method instead of

directly printing to stdout.  This was a bit more work than it sounds like
it should have been:
  * turned 'select_pattern()' and 'exclude_pattern()' from functions into
    methods, so they can refer to 'self' to access the method
  * commented out the *other* 'exclude_pattern()' method, which appears
    to be vestigial code that was never cleaned up when the
    'exclude_pattern()' function was created
  * changed the one use of the old 'exclude_pattern()' method to use the
    new 'exclude_pattern()' (same behaviour, slightly different args)
  * some code and docstring reformatting
  * and, of course, changed all the debugging prints to 'debug_print()' calls
Added/tweaked some regular ('self.announce()') output for better runtime
  feedback.