ShrinkUrl: use x0 by default. Fixes #617.

x0 has the smallest working output. ur1 had the second smallest.
Their difference is one character.
debian/control: Replaces supybot

It was just said at #Limnoria that someone couldn't install Debian packages
 of Limnoria, because haven't been configured to replace supybot.

NOTE: I am not Debian packager, so I have no idea if this works, so please
test it first!
Fixes ProgVal/Limnoria#611
Merge pull request #622 from ncoevoet/master

Fixes ProgVal/Limnoria#611
Merge pull request #620 from Mkaysi/debian

debian/control: Replaces supybot
Merge pull request #619 from Mkaysi/shrinkurl

ShrinkUrl: use x0 by default.