[Pinterest] Add implementation for user/board
[Pinterest] Add implementation for user/board

The data is no longer provided in HTML upon request,
but rather encoded as JSON in a SCRIPT section and
decoded via Javascript on the client side. The bridge
now decodes the data and returns valid feeds again.

Riduidel/rss-bridge,RSS-Bridge/rss-bridge,simonbru/rss-bridge,Riduidel/rss-bridge,kranack/rss-bridge,ORelio/rss-bridge,Frenzie/rss-bridge,teromene/rss-bridge,LogMANOriginal/rss-bridge,Frenzie/rss-bridge,teromene/rss-bridge,simonbru/rss-bridge,sebsauvage/rss-bridge,kranack/rss-bridge,LogMANOriginal/rss-bridge,ORelio/rss-bridge,kranack/rss-bridge,mro/rss-bridge,RSS-Bridge/rss-bridge,griffaurel/rss-bridge,GregThib/rss-bridge,kranack/rss-bridge,Riduidel/rss-bridge,mro/rss-bridge,ORelio/rss-bridge,RSS-Bridge/rss-bridge