Release Notes: 0.5.8

What's new since 0.5.7?

Updated git to 2.34.0 for the helper.
Python 3.5 and newer are now officially supported. Git-cinnabar will try to use the python3 program by default, but will fallback to python2.7 if that's where the Mercurial libraries are available. It is possible to pick a specific python with the GIT_CINNABAR_PYTHON environment variable.
Fixed compatibility with Mercurial 5.8 and newer.
The prebuilt binaries are now optimized on arm64 macOS and Windows.
git cinnabar download now properly returns an error code when failing to extract the prebuilt binaries.
Pushing to a non-empty Mercurial repository without having pulled at least once from it is now prevented.
Replaced the nagging about fsck with a smaller check always happening after pulling.
Fail earlier on git fetch hg::url <sha1> (it would properly fetch the Mercurial changeset and its ancestors, but git would fail at the end because the sha1 is not a git sha1 ; use git cinnabar fetch instead)
Minor fixes.