[FT] Use new 3.0 version of `flix-tech/avro-php` (flix-tech#24)

[CI] Use wikimedias Avro library (flix-tech#22)

[FX] Fixing dealing with exceptions wrapped in fulfilled promises (fl…

…ix-tech#15)

[RELEASE][HOTFIX] Correct Stream processing with newer Guzzle versions (

flix-tech#14)

* [FX] Also add throwing values in rejection callbacks

* [FX] Also add throwing values in rejection callbacks for CachedRegistry

* [FX] Use correct stream string access in `ExceptionMap`

[FX] Use correct stream string access in `ExceptionMap`

[FX] Also add throwing values in rejection callbacks for CachedRegistry

[FX] Also add throwing values in rejection callbacks

[FX] Use correct way of retrieving the contents of a Guzzle stream (f…

…lix-tech#13)

Replace `flix-tech/avro-php` instead of `rg/avro-php` to fix critical…

… bug (flix-tech#12)

The bug made it impossible to deserialize binary encoded messages
which contained `array` and `map` data types in their schemas

[RELEASE] Prepare docs for 4.0 release