[YouTube] Consider capturing short URLs

[beefchimi]

Previously, I was simply capturing youtu instead of the full youtube in order to match against the shortened youtu.be URLs.

youtu.be URLs do not currently support user channels, and are instead meant for short linking to videos. If we match for just /youtu/ - and make matching /(channel|c)/ optional - we will end up capturing anything in the first path segment.

This could be desired functionality... if consumer's want to consider a "watch URL" a sort of "social handle". I would need to further explore this use-case before I go ahead with it.