ao_jack: increase buffer size, always round up buffer size

This should help with github issue #128, which reported stuttering
distorted sound with 6 channel audio, but not with 2 channels.
ao_jack: allow more control about channel layouts
core: make network options available even if old net code is disabled

Preparation for removing the old network code.
Remove internal network support

This commit removes the "old" networking code in favor of libavformat's
code.

The code was still used for mp_http, udp, ftp, cddb. http has been
mapped to libavformat's http support since approximately 6 months ago.
udp and ftp have support in ffmpeg (though ftp was added only last
month). cddb support is removed with this commit - it's probably not
important and rarely used if at all, so we don't care about it.
manpage: fix section headings
stream: re-add accidentally removed seek call

This was under CONFIG_NETWORKING, so in theory it should have been save
to remove. But actually this disables forward skipping when reading
from a pipe. (Still a questionable feature, because it doesn't behave
well with libavformat - but it was not supposed to be changed.)
stream: remove weird STREAMTYPE_STREAM special handling

This was an old leftover from an earlier cleanup (which happened in
2003), and which used "special" stuff for streams that could be only
forward-seeked.

Also, don't add mode flags to s->flags; they're supposed to be in
s->mode instead.
Remove some leftovers from network removal

stream_vstream.c in particular was actually dependent on the network
code, and didn't compile anymore.

Cleanup the protocol list in mpv.rst, and add some missing ones
supported by libavformat to stream_lavf.c.
stream: don't treat position 0 specially

Seeking to position 0 meant to try reconnecting with some streams,
actually just the internal http implementation. This has been removed,
so we don't need the special handling anymore.

This means we don't have to be stuck in a retry loop if the stream
doesn't even support reconnect.
configure: prune some more crap

All of the removed lines are hopefully useless and didn't do anything.
configure: simplify arch macros
osdep: remove unused mmap compatibility hacks

Not sure how this worked. Only af_export.c and tvi_v4l2.c were
using mmap, but they didn't include osdep/mmap.h or mmap_anon.h. In
any case, we trust that the target system is sufficiently POSIX
compliant if mmap is actually defined (as checked by configure).
stream: unbreak streams with large sector sizes (stream_cdda)

Commit 7b16d4b changed some stream implementations to check the buffer
size passed to them. This made stream_cdda stop working, because the
default buffer size is smaller than the CDIO frame size. So pass the
sector size instead of the (arbitrary) default buffer size.
Remove old demuxers

Delete demux_avi, demux_asf, demux_mpg, demux_ts. libavformat does
better than them (except in rare corner cases), and the demuxers have
a bad influence on the rest of the code. Often they don't output
proper packets, and require additional audio and video parsing. Most
work only in --no-correct-pts mode.

Remove them to facilitate further cleanups.
demux: remove audio parser

The audio parser was needed only by the "old" demuxers, and
demux_rawaudio. All other demuxers output already parsed packets.

demux_rawaudio is usually for raw audio, so using a parser with it
doesn't usually make sense. But you can also force it to read
compressed formats with fixed packet sizes, in which case the parser
would have been used. This use case is probably broken now, but you
will be able to do the same thing with libavformat demuxers.
demux: remove some old stream header functions
demux: remove video_read_properties
demux: remove unused function
demux: merge functions
demux: remove separate arrays for audio/video/sub streams, simplify

These separate arrays were used by the old demuxers and are not needed
anymore. We can simplify track switching as well.

One interesting thing is that stream/tv.c (which is a demuxer) won't
respect --no-audio anymore. It will probably work as expected, but it
will still open an audio device etc. - this is because track selection
is now always done with the runtime track switching mechanism. Maybe
the TV code could be updated to do proper runtime switching, but I
can't test this stuff.