Fix pointer type warning by casting the argument (it expects a const).
Issue #24: Added avbin_get_info() function.

Added the avbin_get_info() function and removed the avbin_get_libav_(commit|version)() functions that I tried out in AVbin 9, which I never really released.

avbin_get_info() returns an AVbinInfo struct with the following members (all strings except where indicated):
- version                // integer, same as avbin_get_version()
- version_string         // includes potential prerelease info, for example "10-beta1"
- build_date             // %Y-%m-%d %H:%M:%S %z
- repo                   // Git URL
- commit                 // Git commit hash
- backend                // "libav" or "ffmpeg"
- backend_version_string // Most recent backend version tag, i.e. "v0.8.3"
- backend_repo           // Backend git URL
- backend_commit         // Backend git commit hash

Also in this commit:
- Updated examples/avbin_dump.c to dump all info from avbin_get_info()
- Fixed the "--fast" option in build.sh so it actually works
- Started using "backend" to refer to libav or ffmpeg stuff, to avoid future renames.
Updated the README with current build and contributor information.
Merge branch 'threads'
Issue #25: For OS X files, made the configure and Makefile options and flags as similar as possible.

I was actually able to get the extra configure flags down to 0 for 64-bit OS X, since that's our primary development platform.

I was able to eliminate a lot of the flags from the Makefiles which were necessary before.  I think the difference was that I recently upgraded to Xcode 4.4 (from 4.2.x, I think) in which I believe Apple switched from using GCC to LLVM under the hood.  Not entirely certain, but whatever the case it makes for cleaner Makefiles.
Updated comments to emphasize avbin_init_threads() with the 0 option.
Included libavutil/mathematics.h to fix the following warning when compiling under linux:  src/avbin.c:386:5: warning: implicit declaration of function ‘av_rescale_q’ [-Wimplicit-function-declaration]
Issue #25: For Linux 32-bit files, reduced the configure and Makefile options as much as possible.  Enabled bz2 and zlib configure options globally.

I don't know why we need -lbz2 for linking, but not -lz.  Perhaps I just don't have a zlib media source to crash at runtime...

Updated the README with some more libraries that you need to install on linux.
Added -lz -- the library size changes when I add it, so it's obviously needed.
Issue #25: For Linux 64-bit files, reduced the configure and Makefile options as much as possible.

The 64-bit Makefile needs one more linking option than 32-bit (-Bsymbolic) and the configure file needs one more option (--enable-pic).

I was able
Issue #25: For Windows (32- and 64-bit) files, reduced configure and Makefile options to a minimum.

The most significant (and embarassing) find I made during these changes were that my win64 environment didn't contain libbz2 and libz.  I fixed that and updated the README to reflect that.

Other than that, I was able to reduce the configure and Makefile options quite a bit.  They ended up nearly identical--other than the prefix/path differences, the only mystifying difference left was that win64 needs two dashes for the "--allow-multiple-definition" option while win32 requires one dash ("-allow-multiple-definition").
Issue #16: Figured out how to create a binary package installer for OS X.