v1.5.0

[DobromirM]

Changes:

1. Downlinks will now reconnect by default when there is a connection failure.
2. Added keep_linked and keep_synced

...

value_downlink = swim_client.downlink_value()
value_downlink.set_host_uri('ws://localhost:9001/')
value_downlink.set_node_uri('/unit/foo')
value_downlink.set_lane_uri('info')

value_downlink.keep_synced(True)
value_downlink.keep_linked(False)

...

3. Added method for waiting until all client tasks are completed. The behaviour is modeled after the [Thread.join interface](https://docs.python.org/3/library/threading.html#threading.Thread.join).
   Fred, This should address the problem that you had.

if __name__ == '__main__':
    swim_client = SwimClient()
    swim_client.start()

    event_downlink = swim_client.downlink_event()
    event_downlink.set_host_uri('ws://localhost:9001/')
    event_downlink.set_node_uri('/unit/foo')
    event_downlink.set_lane_uri("publishValue")
    event_downlink.on_event(custom_on_event)
    event_downlink.open()

    # This is used to block the thread until all client tasks have completed
    swim_client.join()

    # Alternatively, a maximum timeout may be provided which will unblock the thread after it has elapsed
    # swim_client.join(timeout=300)

4. Added custom errors for trying to open a downlink before first setting the host, node or lane. Closes Error messages for invalid downlinks #53