Post History

Fix pushed.

When you save a post, we don't take what you typed into the textbox and convert it to markdown on the server, if we can avoid it (we still have to if the client has JS disabled). There's this live preview below the textbox where the HTML has already been calculated for us, so we might as well make use of that; we actually take that HTML and save it instead of re-processing it. This both saves server time and avoids conflicts or formatting differences between client-side and server-side markdown rendering, so it's good all round.

_However_, that relies on us actually having rendered that markdown client-side at that point. Which, in this case, we hadn't done, because it was only re-rendered on `keyup`, `focus`, and `markdown` events. I've adjusted it to re-render on `paste` and `change` as well, so that should capture most changes.