Robotframework-confluentkafkalibrary

* Added Purge keyword

Fixes:
* Removed deprecated arguments
* Tests updated

Devops part:
* Github actions are now used for build, test and publish. ( travis.ci removed)

- Support confluent-kafka-python [v1.5.0](https://github.com/confluentinc/confluent-kafka-python/releases/tag/v1.5.0)
- legacy still supported
- new keywords
- new [example of serializers](https://github.com/robooo/robotframework-ConfluentKafkaLibrary/blob/master/examples/test_avro.robot#L48)

Fixes:
- Fix for RobotNotRunningError exception (nczita, https://github.com/robooo/robotframework-ConfluentKafkaLibrary/pull/15)
- Optional exception throwing if the deserialization fails (tminakov, https://github.com/robooo/robotframework-ConfluentKafkaLibrary/pull/13)
- Add dependencies to setup.py (nczita, https://github.com/robooo/robotframework-ConfluentKafkaLibrary/pull/14)
- Support for newer Robotframework versions (tminakov, https://github.com/robooo/robotframework-ConfluentKafkaLibrary/pull/9)
- remove the package as dependency, it's in the standard library (tminakov , https://github.com/robooo/robotframework-ConfluentKafkaLibrary/pull/11)


Devops part:
- automated creation of documentation, release and publishing of latest test results

Bugfixes:
* Fixed unfunctional avro producer
* encoding of data was removed by default (could cause problems if user encode / decode on his side)
* List of topics available for consumer and producer too
* Remove remove_zero_bytes from _decode_data, if needed user should this by themselves

New features:
* Tags + releases of this lib will be same as in confluent-kafka repository + with related bugfixes/features e.g. 1.3.0 == 1.3.0
* new bugfixes and features will be defined after '-' e.g. 1.3.0-1, 1.3.0-2....
* new methods included see documentation at https://robooo.github.io/robotframework-ConfluentKafkaLibrary/