Split the interface definitions out into a separate module.
Split the really obvious eliot-related code out into a separate module.
Make the tests pass even if eliot is not importable (and keep them passing if it is).
Document the optionalness of eliot.  Declare this to the packaging and testing systems, too.
Add another test configuration.
Consistently use block string literals to avoid falling into yaml traps.
Add additional logic to disable logging when eliot is installed but too old.
Add missing module boilerplate.
Use a construct that does not appear to fail.  Failure of install steps causes travis to mark the job as "errored".
add a docstring for _isTerminal
delete some trailing whitespace
add a missing word
merge master
news fragment
Merge pull request #31 from hybridlogic/retry-optional-eliot-6

Eliot is now optional.  Transitions will be logged if and only if it is available.