x86-64: cabac_block_residual assembly

RDO: ~20% faster than C
Bitstream: ~50% faster than C
1-2% faster overall, highest on preset superfast/fast/medium.
Add slice-min-mbs feature

Works in conjunction with slice-max-mbs and/or slice-max-size to avoid overly
small slices.
Useful with certain decoders that barf on extremely small slices.

If slice-min-mbs would be violated as a result of slice-max-size, x264 will
exceed slice-max-size and print a warning.
Add slices-max feature

The H.264 spec technically has limits on the number of slices per frame. x264
normally ignores this, since most use-cases that require large numbers of
slices prefer it to. However, certain decoders may break with extremely large
numbers of slices, as can occur with some slice-max-size/mbs settings.

When set, x264 will refuse to create any slices beyond the maximum number,
even if slice-max-size/mbs requires otherwise.
x86inc: fix some corner cases of SWAP

SWAP with >=3 named (rather than numbered) args
PERMUTE followed by SWAP with 2 named args
used to produce the wrong permutation
Fix undefined behavior in x264_ratecontrol_mb
Fix array overreads that caused miscompilation in gcc 4.8
x86inc: create xm# and ym#, analagous to m#

For when we want to mix simd sizes within one function.
x86: correctly check stack alignment for Atom hadamard_ac

Regression in r2265 (only affected compilers with broken stack alignment,
like ICL on win32).
Get audio from AvxSynth as well.

Based on a patch by 0x09 (tab@lavabit.com). The original patch
description as follows:

In this case since they both target 2.5, the only modifications
to input/audio/avs.c are linking av[ix]synth instead of loading,
and not being usable as an importer for regular audio files (only
scripts)*.

*The other one allows things like

--audiofile somefile.mp3 --ademuxer avs

and opens somefile with (e.g.) DirectShowSource. Since all we have
is ffms2 it's kind of pointless.
More detailed version head
Fix compilation with --disable-audio
Skip useless lavr check when lavf is not available
Add an option to use r2204 style progress indicator
Add back "touhou" tune
Film Grain Optimization
Fade Compensation
Remove stats before renaming
Add a parameter to set level of writing options in User Data Unregistered SEI
Utilize internal threading in lavf/ffms
Auto VBV settings