Allow posting a full thread

[Oblomov]

Before some recent changes, I had a custom patch that allowed me to write a full thread and have too post it as a sequence of posts, each in reply to the previous (and optionally the first in reply to some user-specified one).

I would like to reintroduce the feature on the new codebase, but before getting to work on the feature I would like to reach a consensus on the user-facing UI. This feature would (in my mind) only be available through the editor.

On my original patch, I was using a simple -- on its own line as post separator in the thread, but this is a horrible choice. Since the choice of separator should be something unlikely to appear in actual text, something more sophisticated is needed.

Personally I would be OK with using control characters (e.g. a vertical tab or form feed), which can be input relatively easy on the three major editors (vim, nano, emacs) in the *nix world, but I'm not sure how welcome this would be. The advantage of accepting control characters is that we could use the standard ^A/^B to isolate the “header” of a post, holding its metadata, something like:

^A
sensitive = True
content-warning = Control codes galore!
^B
This is the actual text of the post
^L
A second post in the thread
^L
^A
content-warning =
^B
A third post, with no content warning.

or something like that