Adding method to detect the edge on the timer expiration.
Added
- Added ``tmrExpiring()`` method to access the expiration event.
- Added some tests, using pytest fixtures, pcaspy server and event queue.
- Automatic testing with nox and gitlab-ci.
- Documentation update.
Changed
- Added ``io.changing()`` now returns ``False`` on the initialization event. Use ``io.initializing()`` instead.