Replace the `jenskins.sh` script using pip with `make_docs.sh` script
expected to run on Ubuntu.

For apt install set non-interactive env variable.

Update CI to run on `ubuntu-24.04` instead of `ubuntu-latest`.

Remove the files `jenkins.sh` and `requirements.txt`

For Sphinx `v8.1.3` compatibility remove the `get_html_theme_path` call.

Fixes: #807

I like to write documentation in MarkDown better than in `*.rst`.

First step is to have new package documentation in MarkDown. So port the
reference `foo.rst` to `foo.md`.

…ist (#811)

When building the docs on Ubuntu 24.04 many deprecation warnings are shown

```
direct use of the spelling directive is deprecated, replace ".. spelling::" with ".. spelling:word-list::"
```

Fixes: #806

Need to use a patched version of `libdeflate` as the created CMake
config contains absolute paths breaking the caching.

Once ebiggers/libdeflate#434 is merged and
released we can use pure upstream.

Fixes: #804

Unpinn OpenCV 4.10 because TIFF 4.7.0 fixes build issues on Linux.
Fixes: #765

Remove old `FindTIFF.cmake` module. Not needed anymore (and probably
wasn't needed for a long time).

Update to use https://github.com/cpp-pm/libtiff/releases/tag/v4.7.0-p0

hunterized dependencies:
- `zlib`: default ON, only dependency available in previous 4.0.2 hunterized version)
- `libdeflate`: default: ON, available in Hunter starting with `v0.26.3` #804
- `jpeg`: default OFF, newly hunterized
- `lzma`: default OFF, newly hunterized
- `zstd`: default OFF, newly hunterized

Not hunterized dependencies:
- `jbig=OFF`
- `lerc=OFF`
- `webp=OFF`

Update the TIFF example to use use `stdio.h` `remove()` instead of `unlink()`.

Fixes: #789