iperf-3.11 release engineering tasks.

Bump version number, update release notes, rename release notes and tweak
markup. Update copyright year.

fix shellcheck warnings

Generate sha256 file automatically so we don't have to copy-and-paste it.

Make this work on old git (1.7).

Roll tarballs slightly differently so we actually get compression.

We were relying on "git archive" being able to create tar.gz files,
but that ability isn't present in the git that comes with CentO

Roll tarballs slightly differently so we actually get compression.

We were relying on "git archive" being able to create tar.gz files,
but that ability isn't present in the git that comes with CentOS 6,
so we use git to create a tar file and then compress it ourselves.

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Try to make make_release work for git. "tar" works, "tag" might.

Minor improvements to make_release script.

Allow optional specification of a version string (the intended use of
this to be able to roll a tarball from a source tree / repo that's not
the exact vers

Minor improvements to make_release script.

Allow optional specification of a version string (the intended use of
this to be able to roll a tarball from a source tree / repo that's not
the exact version being released).

Compute and display SHA256 hash of the tarball on Linux, FreeBSD, and
MacOS.

Don't exclude make_release from the tarball (no point in hiding it)
but do try a little harder to get rid of .hg\* files.

Comment out some debugging code.

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cleanups on the make_release script

update make_release for hg

add make_release script