HTJ2K decoding + github action workflows

[Even Rouault]

Hi,

some good news to share about latest developments in OpenJPEG master branch:

- Aous Naman has made a great contribution by adding a HTJ2K (High
Throughput / Part-15) decoder. See
https://github.com/uclouvain/openjpeg/pull/1381 for details and
limitations. My quick experiment (see
https://github.com/uclouvain/openjpeg/pull/1374#issuecomment-926894225)
shows a ~ x2 speed improvement in mono-threaded decompression compared
to regular Part-1 code block style.

- I've migrated most of the continuous integration target to github
action workflows. The driver for this is that Travis-CI is no longer
friendly to open source projects due to a limited small quota that was
exhausted for our project. github action workflows are naturally
inherited in forks, so you can potentially work on a branch for some
time, push in your clone, check CI results and just issue a pull request
when you're done.

Even

--
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My software is free, but my time generally not.