New port, multimedia/rubygem-paperclip-av-transcoder: Audio/Video
transcoder for Paperclip using FFMPEG/Avconv

Adding this because it is a dependency of the upcoming www/mastodon port.

WWW: https://github.com/ruby-av/paperclip-av-transcoder/

Approved by: swills (mentor, implicit)
Differential Revision: https://reviews.freebsd.org/D10350