This adds pinterest as an option on social icons, and adds per-slide sharing links.

The code might be mental. if it is, i am sorry.

RFC
Yeah, I suppose I don't know if we'll ever need it. But it's nice that if there is a page where, for example, the stumbleupon icon makes more sense displayed somewhere other than the social bar we can just pass `hide: ['stumbleupon']`

i'm glad i found this code. i thought i'd chee'd it, i wrote it a few weeks ago in rockton.