elinks supports SpiderMonkey 78 (from 2020) and not only 1.5 (from
2000). This is not documented yet.
Removed `js-1.5-rc6a+elinks.patch` because the Meson build script expect
SpiderMonkey 78 for which this patch is irrelevant. Also, you can build
elinks with the vanilla SpiderMonkey 78, that is without needing to
apply any patch.
Removed the documentation on building SpiderMonkey 1.5 because this is
not relevant anymore.
Updated the documentation to use `meson build` instead of `autogen.sh`.
I think the autogen.sh doesn't yet support new SpiderMonkey versions.
