Improving event subscription interface

README.md

tangostationcontrol/VERSION

tangostationcontrol/tangostationcontrol/common/asyncio.py

...ontrol/tangostationcontrol/common/events/change_events.py

...ontrol/tangostationcontrol/common/events/subscriptions.py

...tationcontrol/devices/base_device_classes/lofar_device.py

tangostationcontrol/test/common/test_events.py

...rol/test/devices/base_device_classes/test_lofar_device.py