libbs2b: Initial frame for libbs2b-3.1.0
libbs2b: Fix LIB_DEPENDS

Fix LIB_DEPENDS. PORTREVISION incremented.

bin/bs2bconvert depends on libogg, libFLAC, and libvorbis with
explicitly specifying each library version number.
libbs2b: committed on the official tree

This is the first appearance on the official ports repository
libbs2b: pkg-config scheme reformation
libbs2b: Prepend category directory