Require cppTango 9.5.0, bump to 9.5.0.dev0, doc fixes

Require cppTango >= 9.5.0, since the next release will be PyTango 9.5.0.

Fix classifier in pyproject.toml so upload to pypi.org doesn't fail (changed after testing on testpypi.org).

Suggest that developers prefer native installations, rather than using Docker. The manual changes to pytest settings are no longer required when running a single test from PyCharm, now that we have pyproject.toml instead of setup.cfg.

Remove AppVeyor badge from readme, as we no longer use it.

Update .devcontainer Docker image to build 9.5.0, which needs newer omniORB. Some issues found with editable install (cannot import tango: ModuleNotFoundError: No module named 'tango._tango'), and aarch64 (omniORB configure fails to detect platform) when testing (not resolved).

Readthedocs now requires a .readthedocs.yaml configuration file, so add one. Also add pin requirements for repeatable docs, as recommended by readthedocs.

Fix various syntax errors and typos in the docstrings.

Example of docs from this branch on readthedocs (temporarily available): https://pytango.readthedocs.io/en/require-950/contents.html