create a tracker object

    * Create a skeleton Django project so that we can run tests that make use of Django settings etc
    * Move the Django specific backend construction logic to a django package
    * Get rid of global (module level) state, allow tracker instances to be created ad-hoc (similar to logging)
    * Improve API and extensibility
Update AUTHORS file
Merge pull request #15 from rocha/carlos-claim-to-fame

Update AUTHORS file
support running integration and performance tests

* Infrastructure for running performance and integration tests
* Basic tests of both types for the MongoDB backend
* Ensure timestamps include tzinfo

Uses "make" to simplify the execution of the various commands.  We could probably integrate with manage.py or setup.py or something more sophisticated in the future if necessary.  For now I wanted to KISS.
introduce nested contexts and integrate with Django

* Support registering nested contexts
* Provide basic Django middleware for tracking requests
Merge pull request #14 from mulby/gabe/event-view

support nested event contexts
rename event to emit
rename track to tracker
Merge pull request #16 from mulby/gabe/rename

change calling convention from verb-noun (track.event) to noun-verb (tracker.emit)
put back in the context manager
fix request/response asymmetry bug in middleware
Merge pull request #17 from mulby/gabe/context-manager

put back in the context manager