Various documentation fixes, merge with website

The html documentation was diff'ed to the current website pages
and all difference were merged into the page they weren't yet
incorporated. This includes lots of small fixes and
improvements.

Signed-off-by: Erik de Castro Lopo <erikd@mega-nerd.com>
libFLAC/lpc_intrin_sse.c : New SSE code to calculate autocorrelation.

Accelerate FLAC__lpc_compute_autocorrelation_intrin_sse_lag_NN routines for
AMD and newer Intel CPUs (means Core i aka Nehalem and newer). Unfortunately
it's slower on older Intel CPUs.

According to tests at HA:

    <http://www.hydrogenaud.io/forums/index.php?s=&showtopic=101082&view=findpost&p=870753>

  CPU                 flac -5           flac -8

  Athlon XP           +5 %              +2.4 %
  Athlon 64 X2        +9 %              +4 %
  Core i              +7 %              +1 % ... +2.7 %
  Core 2              ?                 -3.5 %

According to Steam HW survey <http://store.steampowered.com/hwsurvey/>
69% of Steam users have SSE4.2 which means that the new code is faster for
them. There are also AMD users that don't have SSE4.2, so 75% of Steam users
should benefit from this patch.

Patch-from: lvqcl <lvqcl.mail@gmail.com>
include/share/endswap.h : Improvements to fallthrough ENDSWAP_*.

According to patch author GCC can optimize expressions like
"(a<<8)|(a>>8)", but has problems with "(a<<8)+(a>>8)".

Patch-from: lvqcl <lvqcl.mail@gmail.com>
libFLAC/cpu.c : Refactor disabling SSE into a single function.

Patch-from: lvqcl <lvqcl.mail@gmail.com>
win_utf8_io.c : Use vsnprintf_s instead of vsprintf.

Patch-from: lvqcl <lvqcl.mail@gmail.com>
win_utf8_io.c : Fix potential memory leak.

Patch-from: lvqcl <lvqcl.mail@gmail.com>
win_utf8_io.c : Remove redundant line.

Patch-from: lvqcl <lvqcl.mail@gmail.com>