implement pre_transition and post_transition callbacks
renamed method for clarity
rename method and vars to reflect that this is a pending StateLog
tests for pre_transition_callback and post_transition_callback
added option to use cache backend or not
update documentation
split pending cache item methods into manager methods

Added tests
fix test for < Django 1.6 compatibility
PEP8 style fixes
created and applied settings configurations
update documentation
pull out methods into two separate managers, renamed methods
apply separate managers to StateLog model
use appconf to set default app settings
use appconf settings throughout app
connect callback functions to signals depending on settings
update tests
only add PendingStateLogManager to model if using cache backend
fix tests
forgot dependency