add shortlink to backcompat classes

[karadaisy]

trafficstars

Discussed in snarfed/bridgy#173 And based on http://microformats.org/wiki/rel-shortlink#Abstract

we should add rel=shortlink like rel=bookmark to the hentry-scoped rel-properties, and also backcompat support for interpreting class=shortlink as class=u-shortlink.

[snarfed]

snarfed/bridgy#173

[karadaisy]

oops, sorry, thank you for catching

[kartikprabhu]

Neither http://microformats.org/wiki/h-entry#Backward_Compatibility nor http://microformats.org/wiki/rel-shortlink defines any backcompat parsing for rel-shortlink

[capjamesg]

I am going to close this issue since it has been inactive for a long period of time without discussion. If this issue is still relevant, feel free to re-open it and we can continue discussing it. Thanks!