Big structure changes (check commit description)

- Moved most of the parser functions/files to the core package.
- Converted tools file to a package and made separate files for similar functions.
- Now all fetcher engines return a Response object
- Instead of selecting an engine to use and passing config to it, we have separate fetcher classes so the user can choose what to use while importing.
- I added a new custom fetcher so the user can create and use an engine.
- More...

scrapling/engines/__init__.py

@@ -1,6 +1,7 @@
 from .camo import CamoufoxEngine
 from .static import StaticEngine
-from .pw import PlaywrightEngine, DEFAULT_DISABLED_RESOURCES, DEFAULT_STEALTH_FLAGS
-from .tools import check_if_engine_usable
+from .pw import PlaywrightEngine
+from .constants import DEFAULT_DISABLED_RESOURCES, DEFAULT_STEALTH_FLAGS
+from .toolbelt import check_if_engine_usable
 
 __all__ = ['CamoufoxEngine', 'PlaywrightEngine']