Jira reader:
* Fixed parsing of autolinks (i.e., of bare URLs in the text).
Previously an autolink would take up the rest of a line, as spaces
were allowed characters in these items.
* Emoji character sequences no longer cause parsing failures. This was
due to missing backtracking when emoji parsing fails.
Jira writer:
* Block quotes are only rendered as `bq.` if they do not contain a
linebreak.
Icons are now converted as follows: `(/)` to ✔, `(x)` to ❌, `(!)` to
❗, `(+)` to ➕, `(-)` to ➖, `(off)` to 🌙, and `(*)` to ☆. The new
icons render well in most fonts. Furthermore, the UTF-8 characters all
fit into 4-bytes.
Closes: #6264
