* API change: the Parser attribute breadcrumbs has been
  renamed to stack.  It was previously undocumented anyway,
  though has now been documented.
* Added the line_number and source attributes to the
  Parser object, for the convenience of pragma handlers.
* Refactored parser_include slightly.  No change to
  functionality or behavior, just a small code cleanup pass.
* Added a "lines per second" output metric to the
  benchmark program.