Respond to full PR/issues URLs

[astorije]

Right now, bot answers to #xxx with PR title, status and links, such as:

<alice>		Look at #1047
<lounge-bot>	[PR 1047] (open) Condense join into nicknames (https://github.com/thelounge/lounge/pull/1047)

But if someone posts the full URL, nothing shows up. The following would be great in addition to the above:

<alice>		Look at https://github.com/thelounge/lounge/pull/1047
<lounge-bot>	[PR 1047] (open) Condense join into nicknames

[xPaw]

Do we still want to do this especially with link previews in Lounge?