Also makes the following changes:

Updates project URL and moves libpthread to a common dependency;
Makes libopus support in libffmpeg-full contingent on selecting the
libopus package, like other external libraries;
Adds note regarding disabling altivec in ppc hard-float;
Reorganizes SIMD sections to be together;
Drops the need to specify decoder=libopus from -full, done by default;
Adds encoder=libopus to custom.

Expand options for libffmpeg-custom:
Build licensing: GPL, GPLv3, LGPLv3
Building for performance or size

Drops version 3 of GPL for -audio-dec, -mini, and -full. Version 3 is
at the discretion of the packager, per:
http://ffmpeg.org/doxygen/trunk/md_LICENSE.html

Add enable-nonfree toggle support to libffmpeg-custom build licensing
to allow inclusion of libfdk-aac.

Use ffmpeg's names for its external libraries in libffmpeg-custom config
Alphabetize same

Correct @BUILD_PATENTED flags for libffmpeg variants

Split libffmpeg-full into hard/soft float:
Hard float configures itself for lame / libx264 using GPL license
Soft float for libshine and LGPL license

Signed-off-by: Ian Leonard <antonlacon@gmail.com>
Signed-off-by: Ted Hess <thess@kitschensync.net>