celery integration basics
rename celery module to avoid absolute/relative import weirdness
move database uri config to ini file
more celery config tweaks for test runs
add a simple test for celery config
add a unit test for the example task
setup celery workers with a mysql connection and isolate it in tests
move database binding out of `on_bound`, as that happens too early
attach database to the correct celery app in each worker process
add a test for task retries
clarify task defaults options

and remove customized options from example task, as there's no need for them
move test task into `tests` sub-package
add an explicit test for task retries
define a new celery+app test base class
implement first non-idempotent version of histogram task