tor-spec: replace Section x.y.z with links
This replaces most of the occurences found with
git grep '[sS]ection\s[0-9]'
in tor-spec.
I left instances inside code blocks for follow-up MRs.
This replaces most of the occurences found with
git grep '[sS]ection\s[0-9]'
in tor-spec.
I left instances inside code blocks for follow-up MRs.