Porting notes:

- tox handles Python environments automatically. Remove a bit of PYTHONPATH
  manipulation (that was using Python 2 code which always failed!)

- No `clean` target: `git clean -xdf` should fit the bill.

- No `reindent` target: the `reindent.py` script it was using does not
  exist (anymore?).

- No equivalent of tox-test-coverage, which was an artifact of the past,
  using nose.  Instead, the test-coverage target only is ported, which
  uses pytest, and works.

* Add support for Python 3.11

* Test Python 3.12-dev

* Add colour to CI for readability

* Drop support for EOL Python 3.6

* Test slower Windows first to speed up CI

Some recent GitHub action runs have started to fail, like

https://github.com/Jean-Abou-Samra/pygments/actions/runs/3642986206/jobs/6150712048

(others don't fail because they pick up Python 3.6 in a cache).

The problem is that GitHub upgraded the ubuntu-latest images to refer
to Ubuntu 22.04, and setup-python doesn't provide Python 3.6 on 22.04,
so use 20.04 for Python 3.6.

#2301 eliminated the lxml dependency, which was the problematic point.

Signed-off-by: Alex <aleksandrosansan@gmail.com>

Signed-off-by: Alex <aleksandrosansan@gmail.com>

* Add Make target for building Pyodide with currently checked out Pygments

Add a target to the documentation's Makefile to make Pyodide with
Pygments from the current checkout.

Additionally, use this target when building the documentation with
the demo page.

The new target works by building Pyodide on a Docker container, and
then exporting the build artifacts back to the host.

The Dockerfile used by the new target is based on the Dockerfile which
was used for building Pyodide on the CI:
https://github.com/pygments/pyodide-artifacts/blob/master/container/Dockerfile

The main difference between the two is that the new Dockerfile uses the
newest Pyodide base image, which is built by a repository which is actively
maintained (the Iodide project is no longer maintained).

The purpose of this change is to allow running the demo locally,
which was not possible previously, as Pyodide was only built by the
CI when deploying to Github Pages.

* Add instructions on how to run the demo locally to the README

* Update demo to work with Pyodide v0.20

Remove usage of Pyodide functionality which was deprecated in Pyodide v0.17:

- Loading Pyodide using `languagePluginURL` and `languagePluginLoader`.
- Access to globals via `pyodide.globals.x` has changed to `pyodide.globals.get("x")`.

Source:
https://pyodide.org/en/stable/project/release-notes/v0.17.0.html?highlight=languageplugin#api-changes

* Fix #2137

* Fix use of `styles` variable before it's defined

The `styles` variable was being used before it's value was set (which
is done when Pyodide finishes loading).

* Remove GitHub action for building Pyodide

This action is obsolete, as building Pyodide is now done using `make pyodide`.

* Upgrade Pages deployment action version

* Add to .dockerignore all files in .gitignore

* Change `pyodide` target to be a phony target