Import cowthinks.
Beeminder.py: handle EOF.
Refactor beeminder.py and accept comments.

- Use stdout instead of stderr for output, and don't print a message for
  every line read.
- Accept arbitrary extra stuff at the end of the line and include it as
  a comment. The main use case here is to add a timezone, which we
  aren't able to parse without a lot of additional work.