Adds "temporal VBR", which should be mostly useful at low bitrate.

The idea is to allow more noise than the default in quiet segments.
Right now, this hurts for high bitrates , so it's gradually reduced
as the rate goes up, until it's completely disabled above 68 kb/s.
Big squashed commit of Garf's MSVC reorg:

commit 77880655f652c54415e4b5f03b5984b951f5267b
Author: Timothy B. Terriberry <tterribe@xiph.org>
Date:   Wed Jun 26 12:23:53 2013 +0200

    Fix version.mk parsing in genversion.bat.

    This was broken by the changes in 0482c82f to make it work with spaces.

    CMD interprets the quotes to mean the argument to FOR is a string,
    not a file name. Instead, we expand the path to a short file name.

    Signed-off-by: Gian-Carlo Pascutto <gcp@sjeng.org>

commit 8e97847ecac3a04956747b117fefef14939cbcbe
Merge: 0482c82 3c0aa8f
Author: Gian-Carlo Pascutto <gcp@sjeng.org>
Date:   Wed Jun 26 12:19:41 2013 +0200

    Merge branch 'master' into msvc_reorg

commit 0482c82fea6dd397a7d2ab50dc6cda4965278fc2
Author: Gian-Carlo Pascutto <gcp@sjeng.org>
Date:   Tue May 21 17:59:30 2013 +0200

    Make genversion.bat work in paths with spaces.

commit 3648ec55b7511119735280fc49bc57c7a3b55d6a
Author: Gian-Carlo Pascutto <gcp@sjeng.org>
Date:   Tue May 21 17:42:14 2013 +0200

    Rework output & intermediate dirs for parallel build support.

commit c367a0fcfcbf5551fb65d61365d9b832d7af2b38
Merge: bafb1dd b518b56
Author: Gian-Carlo Pascutto <gcp@sjeng.org>
Date:   Tue May 21 14:17:11 2013 +0200

    Merge branch 'master' into msvc_reorg

    Conflicts:
    	win32/VS2010/celt.vcxproj
    	win32/VS2010/opus.vcxproj
    	win32/VS2010/silk_common.vcxproj
    	win32/VS2010/silk_float.vcxproj

commit bafb1dda3fcf6785decdfb42a1f934c7fab0c567
Author: Gian-Carlo Pascutto <gcp@sjeng.org>
Date:   Mon Mar 11 21:25:28 2013 +0100

    Fix two more files to not have the Platform Toolset explicitly set.

commit c69c870201fec7461862fe79731a37866a1810f1
Author: Gian-Carlo Pascutto <gcp@sjeng.org>
Date:   Mon Mar 11 21:08:00 2013 +0100

    Add missing SILK MSVC project files.

commit a0d41fb7f97558c8f812d500b9027c77907c37c0
Author: Gian-Carlo Pascutto <gcp@sjeng.org>
Date:   Fri Mar 8 15:00:51 2013 +0100

    Use the default toolset in the MSVC project files.

commit 34aac5b2637ed38c5620f0d876e08db232849933
Author: Gian-Carlo Pascutto <gcp@sjeng.org>
Date:   Fri Mar 8 14:54:41 2013 +0100

    Move the MSVC project files outside the source tree.

    Bring the project structure more in line with the one in libogg.
Fixes MSVC warnings
Updates the Makefile.am EXTRA_DIST for the MSVC reorg
Avoid name clash with y0 Bessel function
Fixes MSVC warning
Fixes more MSVC warnings
More autoconf housekeeping

Drop the test for getopt, it's not used anywhere anymore.

Switch the last uses of AC_TRY_COMPILE to AC_COMPILE_IFELSE now.
The former is marked as obsolete, and this will leave no confusion
about which to cut and paste if new tests are added.

Double quote all the parameters to AC_LANG_SOURCE and AC_LANG_PROGRAM.
This is actually required, even if you can get away with not doing it
sometimes, so again set a good example for future changes to follow,
to hopefully avoid people getting bitten harder than they need to be.

Don't bother checking for alloca if we're never going to use it
(ie. if we have C99 variable-size array support).
The test for this is a bit sketchy anyway ...  we separately test for
HAVE_ALLOCA_H and USE_ALLOCA, but the test for USE_ALLOCA depends upon
having alloca.h present, yet the use of these macros in stack_alloc.h
only tests for HAVE_ALLOCA_H inside of a test for USE_ALLOCA.
I'm not going to change this logic right now, since I don't know what
crazy system it was attempting to cater for, though I suspect it was
one that was not using the autoconf build system ... since with the
current test that combination should not be possible to obtain.

Use LT_LIB_M instead of the song and dance with testing for exp().
This should also work for BeOS which is what the exp test was added for.
It also means we don't unconditionally add -lm to everything via LIBS.

Use LIBM now instead of hardcoding -lm everywhere.

Use AS_HELP_STRING to format all option descriptions.

Don't bother to test for doxygen if using it is --disable'd.

Drop the SYMBOL_VISIBILITY export, it isn't used anywhere (we add the
compiler flag to CFLAGS).
Replace INCLUDES with AM_CPPFLAGS

Automake 1.13 complains that INCLUDES is obsoleted now.
Make the parallel test mode of automake 1.13 useable
Fixes some return without va_end in the api, adds tests.

Also makes the CTL bad argument handling more consistent to avoid mistakes
 like that in the future.  Also updates the variable duration docs.
Brace a number of if statements instead of one-lining them.
Braces go on the next line.
Add a couple minor additional decoder tests.
Get rid of PC_LIBM

It only existed to not include -lm in the .pc for fixed point builds,
but that is still needed since the float API is still enabled and
will use at least lrint.
Temporal VBR tuning

Applies temporal VBR up to higher bitrates after IgorC reported it being
useful at 64 kb/s for amount=0.1
Adds some checks to the surround API
Disables temporal VBR for LFE
Commenting the speech/music Markov code
More speech/music detection comments (delayed decision)