pybotx` library was rewritten to achieve the following goals:
* Make it easy to maintain (adding new events and methods)
* Separate `pybotx` models from `botx` API for better abstraction
* Make tests simpler, check real code instead of many mocks
* Use incoming message context for `answer` method
* Add `undefined` value for fields that can be skipped in payload
* Drop unused sync client
* Drop DI system, which was incomplete (no `yield` support) and hard to maintain
* Drop next steps (`pybotx-fsm` solve this task)