Official releases moved to GitHub and packagecloud / APT repository now available

[DRC]

libjpeg-turbo was originally hosted entirely on SourceForge. In
response to a weeks-long SourceForge Subversion outage in 2015, I moved
our code repository and issue trackers to GitHub (and spent many unpaid
hours converting our cherry-picked Subversion branch structure to Git
merge commits, etc.) I then moved our mailing lists to Google Groups in
2017 because SourceForge removed the ability for project admins to
view/manage mailing list subscribers. However, I continued to host our
official releases on SourceForge because I didn't have time to move them
and because of the lack of good (free) alternatives for YUM repository
hosting. SourceForge has unfortunately become more flaky in recent
years, and on multiple occasions, our releases have temporarily
disappeared, I have temporarily been unable to upload a new release, and
the YUM repository has temporarily become unusable. The latter two
issues both re-occurred in the last two weeks, which prompted me to
finally bite the bullet and abandon SourceForge.

Fortunately packagecloud is generously providing free hosting for our
new YUM repository, and their platform allows me to host an APT
repository as well. Although GitHub lacks some of the features that I
liked about the SourceForge file release system (such as tracking the
number of downloads in an arbitrary date range for each file and
directory, hosting arbitrary directory structures, and file/directory
management via SSH and SCP), the upside of hosting official releases on
a more stable site that already hosts our code and trackers outweighs
the downsides.

Refer to:
https://libjpeg-turbo.org/Downloads/YUM
for instructions regarding the use of the new YUM and APT repositories.

All of the files that were previously hosted on SourceForge are now
provided as assets under the associated libjpeg-turbo release:
https://github.com/libjpeg-turbo/libjpeg-turbo/releases
All relevant notes from the README files on SourceForge (e.g. change
logs for the packages themselves) have been incorporated into the GitHub
release notes.

Existing releases (3.0.1 and earlier) will remain available on
SourceForge and in the old (SourceForge-hosted) YUM repository, but new
releases from this point on will be uploaded only to GitHub and
packagecloud.

Please let me know if you have any questions or encounter any issues.

DRC