B3: registers :logseq.class/Project and :logseq.class/Area as
built-in page-like classes (the TODO in class.cljs already asked for
this), so users can tag pages/journals with them out of the box.
Fixed a markdown-mirror test whose "Custom Tag" fixture used to be
titled "Project" and collided with the new built-in class.
B4: adds :logseq.class/Citation plus /target and /context properties,
following the :logseq.class/Comments pattern. Since target is a
:node-typed ref, citation blocks automatically show up in the
existing block/citation reference graph without any changes there.
Dasemu
b67f7e9f78