Log instance caching timeout is too low

[François GUÉRIN]

Hi,

While debugging an application using django-fsm-log, an error occurs at the end of the transition process, about the cached log instance is None, as the timeout only 10 seconds, which is too low for a "normal" debugging session.

I' would be nice to make this timeout configurable (for debugging purpose), and to get it from django settings.

I'll propose a PR for this...

Thanks !

[Nicolas Delaby]

I'm not opposed to make the cache duration configurable.
I never used the CacheBackend in our projects. I can't tell much. Feel free to make a pull request and we will take it from there.