Python-logstash-async

* Flush all pending events on shutdown

* Docs: Explain the differences to FileBeat (44)
* Close TCP socket on connect timeouts
* Add Flask formatter

* Fix broken transport instantiation if callable is used (42)
* Fix tcp input codec in documentation

* Add new constant QUEUED_EVENTS_BATCH_SIZE to limit events sent once
(related to 31)
* Add "Beats" transport (logstash-input-beats, related to 31)
* Add "timeout" argument to transport classes for more flexible
setting
* Docs: better document the shared database between handlers (30)
* Perform tests also against Python 3.7
* Docs: explain Formatter extra dict in more detail (23)
* Docs: minor improvements

* Handle possible non-bytes result in Formatter (18, rmihael)

* Implement rate limiting of LogProcessingWorker error messages
* Add a constant to configure the timeout for the Sqlite database