decoder: fix unused-but-set warning

Signed-off-by: Jean-Marc Valin <jmvalin@jmvalin.ca>
Add a comment describing the block size storage scheme

Signed-off-by: Jean-Marc Valin <jmvalin@jmvalin.ca>
Add SSE versions of SAD.

Only handles xstride==1 and square block sizes for now.
Ultimately something will need to be done about the alignment of
 the width-16 versions.

Timing results from
bench.sh ./examples/encoder_example akiyo_qcif.y4m -k 256 /dev/null

Unmodified encoder:
31218 ms (stddev 28) [31169 31182 {31193 31196 31206 31240 31256} 31486 31599]

With this patch:
18134 ms (stddev 103) [17998 18028 {18034 18072 18073 18237 18255} 18282 18398]

Fast motion estimation options (level_max = 0, no chroma ME, no
 subpel refinement):
11044 ms (stddev 5) [11021 11036 {11040 11041 11042 11043 11052} 11053 11054]

Fast ME + patch:
2610 ms (stddev 2) [2602 2603 {2608 2608 2610 2610 2612} 2613 2651]

Signed-off-by: Timothy B. Terriberry <tterribe@xiph.org>
Actually add the new files from the last commit.

git am failed because of fuzz so I used patch... which of course
 didn't do this for me.
Hate you git.
So much.
Fix unix Makefile for 340a45a9 and 446bb396.

Yay continuous integration.
Fix ASM / C mismatches in mc.c introduced in bc5eee37.

r=derf
Add OD_ASSERTs to OD_CHECKASM so that failures are fatal.

I had delayed adding these until all checks were passing again, since
 this will make the CI fail when there is C / ASM disagreement.
Add OD_ASSERTs to od_mc_compute_sad_check so that failures are fatal.
Factor out `od_decode_block_sizes`.

This trims down `daala_decode_packet_in` a bit more.

The functionality for initializing the border as 32x32 was also factored
out into `od_state_init_border_as_32x32`.

No intended functionality change. This is deliberately "verbatim" in the
way it pulls the code out to ease review.

Signed-off-by: Jean-Marc Valin <jmvalin@jmvalin.ca>
Updated version of the PVQ doc (now 33% less wrong)
Plugs in new PVQ code in the encoder (disabled by default)

There's still no decoder and it doesn't produce a complete bit-stream,
but it's now possible to experiment.
Encodes the PVQ prediction flags, which were missing from the bitstream