Add extlinks for Launchpad + contrib update

[rkratky]

Adds roles:

• lpsrc for linking to Ubuntu packages on LP
• lpbug for linking to LP bugs
• associated contrib docs

[s-makin]

this is a really good idea, is it possible to add one for LP teams as well?

Also, for the LP bug one, do people need to include the # as they normally would?

[rkratky]

is it possible to add one for LP teams as well?

Yes, but it's not ideal because LP teams use the https://launchpad.net/~team-name URLs. IOW, there's nothing that would distinguish that URL from users and projects (all of these use the ~<name> format). So, while we can have a shortcut for all of these, there's no way to determine whether the link is to a team, user, or a project.

Also, for the LP bug one, do people need to include the # as they normally would?

No. Also (I didn't include it in the doc), these behave like all other roles, so you can do, e.g.:

{lpbug}`bug no. 12345 & its fancy link text <12345>`

[s-makin]

Makes sense, thanks for the clarification!