Eliminate the C wrappers.

BufferedSocket has just an input buffer, and FullyBufferedSocket adds
the output buffer.

Don't use va_list.

Add the interface ArchiveVisitor.

Drop support for the old faacDec* API.

Fixes build errors on systems without libfaad, when --disable-aac was
not specified.

Some of these are not implemented properly and never worked.  And the
others are not useful; you can easily set environment variables
instead.

Eliminate input_stream_init() and input_stream_deinit().