installation: moved from setup.py to pyproject.toml:

- updated installation to use the now standard `pyproject.toml` instead of legacy
`setup.py`. `setup.py` and other legacy files have been deleted.
- removed outdated README4PACKAGERS
- removed pylintrc which has not been correctly reviewed. Linter conf should go to
  `pyproject.toml` now.
- [hatch](https://hatch.pypa.io) is now used as main building tool. However, thanks to the
use of standards, other tools can be used too.
- update .hgignore
- several dependencies version bump, with code update to adapt to changes.

twisted/plugins/libervia_backend_plugin.py

@@ -44,7 +44,7 @@ class Options(usage.Options):
 
 
 @implementer(IPlugin, IServiceMaker)
-class SatMaker:
+class LiberviaMaker:
 
     tapname = C.APP_NAME_FILE
     description = _("%s XMPP client backend") % C.APP_NAME_FULL
@@ -73,4 +73,4 @@ class SatMaker:
         return LiberviaBackend()
 
 
-serviceMaker = SatMaker()
+serviceMaker = LiberviaMaker()