Merge pull request wpietri#41 from OverloadUT/subscribe

Add event emitters, error handling, vacuum state and lifespan tracking

releasing 0.8.4

Merge pull request wpietri#19 from wpietri/fix-tests-and-deployment

Fix tests and deployment

updates for 0.8.2 release, incluing PyPi support

Updating docs for new release.

Minor tidying.