Configuration and structural changes

A few edits in this pull request:

1. Configuration for GeoJSON file, email recipients and Mailgun account moved to `config.ini`.
2. Local changes files now created by `tempfile.mkstemp()`.
3. Removed dependency on PIL after making ModestMaps python tolerant of its absence in 1.4.2.
4. Added support for cURL in place of wget, at least one should be present on most systems.

Most of this has been done to make the script easier to configure. You’ll also notice that many of the options in `config.ini` can be overridden with environment variables: this is a nod to Heroku which carries its configuration specifics there. I’ve tested changewithin on Heroku and it works fine.