libre 0.4.8 (new formula)

Libre is an Open Source Protocol Library for Real-Time Communications.
It includes protocols like SIP, SDP, RTP/RTCP, DNS, BFCP, STUN/TURN/ICE,
HTTP, Websockets.

This commit adds a new package for libre version 0.4.8

For more information:

    http://www.creytiv.com/re.html
update libre formula

updated after review comments from Mike McQuaid

- use double quotes for depends_on
- add prefix to make invokation
libre: add 0.4.8 bottle.