Add tests for ForeignKey fields with ModelTracker
Added test_number_of_queries in ModelTrackerTestCase
Change failing test to pass for ModelTracker
Create FieldTracker that mirrors ModelTracker
Fix foreign key tests for FieldTracker
Don't compare FK instances in FieldTracker
Improve docstrings and variables for FieldTracker
Change FieldTracker ``current`` for unsaved model

Return None values instead of an empty dict
Fix FieldTracker's has_changed (fixes gh-51)

The FieldTracker has_changed method no longer returns True for any input
when the instance is unsaved and no longer raises a FieldError for
fields after the first save.  The original ModelTracker behavior is
maintained.
Improve FieldTracker docstrings
Update README file for new FieldTracker
Merge branch 'master' into fk-fix

* master:
  Remove misinformation from changelog; oops.
  Tweak AUTHORS and changelog.
  PassThroughManager calls superclass `get_query_set`.
  Update AUTHORS and changelog.
  Fix tox.ini so runtests.sh works.
  Test and fix for second grandchild bug.
Doc updates for FieldTracker -> ModelTracker transition.
Add tests for tracking non-field attributes
Round numbers that Python 2 and 3 agree on