* no longer depend on apt.llvm.org, instead we rely on a zig-bootstrap
tarball with pre-built Zig, LLVM, LLD, and Clang. Similar to the
Windows Dev Kit but for Linux. This also makes the script no longer
depend on Docker, libxml2, or GCC.
* remove bash retry logic; it was only needed for flaky apt.llvm.org
and isn't needed for the other resources we download.
* build and upload the experimental std lib automatically generated
docs. langref.html is moved to docs/langref.html because the std lib
docs are in docs/std/.
* the superfluous "zig" directory in $prefix/lib/zig/std/std.zig is
removed from the tarball.
* update_download_page makes a commit in the www.ziglang.org repository
updating data/releases.json so that repository can manage deploys.
Each of the 3 CI services now trigger a sr.ht build via
the on_master_success script. The sr.ht build checks if all builds have
completed successfully by trying to download the JSON file for the
particular version. If all builds have completed successfully then this
sr.ht job will update the download page.
