Merge branch Davi0kProgramsThings:fix/refactoring into branch bitfinexcom:master. (#238)

# Description
<!--- Describe your changes in detail -->
PR includes some global refactoring in preparation for the v3.0.0 stable release.

## Motivation and Context
<!--- Why is this change required? What problem does it solve? -->
-

## Related Issue
<!--- If suggesting a new feature or change, please discuss it in an issue first -->
<!--- If fixing a bug, there should be an issue describing it with steps to reproduce -->
<!--- Please link to the issue here: -->
PR fixes the following issue: -

## Type of change
<!-- Select the most suitable choice and remove the others from the checklist -->

- [X] Bug fix (non-breaking change which fixes an issue);

# Checklist:

- [X] I've done a self-review of my code;
- [X] I've made corresponding changes to the documentation;
- [X] I've made sure my changes generate no warnings;
- [X] mypy returns no errors when run on the root package;
<!-- If you use pre-commit hooks you can always check off the following tasks -->
- [X] I've run black to format my code;
- [X] I've run isort to format my code's import statements;
- [X] flake8 reports no errors when run on the entire code base;

bfxapi/websocket/_client/bfx_websocket_inputs.py

@@ -1,5 +1,5 @@
 from decimal import Decimal
-from typing import Any, Awaitable, Callable, List, Optional, Tuple, Union
+from typing import Any, Awaitable, Callable, Dict, List, Optional, Tuple, Union
 
 _Handler = Callable[[str, Any], Awaitable[None]]
 
@@ -23,6 +23,7 @@ class BfxWebSocketInputs:
         cid: Optional[int] = None,
         flags: Optional[int] = None,
         tif: Optional[str] = None,
+        meta: Optional[Dict[str, Any]] = None,
     ) -> None:
         await self.__handle_websocket_input(
             "on",
@@ -39,6 +40,7 @@ class BfxWebSocketInputs:
                 "cid": cid,
                 "flags": flags,
                 "tif": tif,
+                "meta": meta,
             },
         )