Implement some recommendations from Raymond H:
Implement some recommendations from Raymond H:

- Make all local variables in the template start with an underscore,
  to prevent name conflicts with the timed code.

- Added a method to print a traceback that shows source lines from the
  expanded template.

- Use that method in main().

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator