audio: Refine interface to introduce infinitely looping sound

The audio library interface is refined to be more C++-ish.

Looping sound loops forever, so the invoker is responsible of stopping
it when the source of sound is destroyed.  The function stopsound3d()
is added to explicitly stop one.
audio: Simplify playWave3D()'s interface

Removed playWave3DPitch() since we can use default parameter in C++.

Also made #ifdef guards do not collide with clib's same header.

Also added some Doxygen comments.
audio: Add volume and pitch change API to audio interface

Using added functions volumesound3d() and pitchsound3d(), you can change
volume and pitch of already running sound source, respectively,
just like movesound3d() for position.
You can make looping sound change attributes after it is initiated,
so convincing effects can be achieved such as varying engine sound
depending on output power.
Remove Win32 from .gitignore file

This is because libogg and libvorbis use the directory name to store
project files.
audio: Import libogg, the container format library for Vorbis

This commit is the first half of Ogg Vorbis support.

The ogg library (libogg) apparently managed with Subversion, but
there's a Git mirror at git://git.xiph.org/mirrors/ogg.git, so we
can subtree merge the library (as we did with clib and cpplib).
I've actually tried that and it worked without a problem, but I
don't think it's worth keeping all the history information of the
library inside our project.  The library is fairly stable and we
can expect that we won't need to frequently update the library.
We just copy the latest source tree under libogg directory,
just like zlib, jpeg, lpng and squirrel3.
audio: Import libvorbis, the lossy audio format library

This commit is the latter half of Ogg Vorbis support.

Now that the container format library is imported, we can import
the library for the content.  It's not coming with history for the
same reason as libogg.
audio: Adapt libogg, libvorbis and libvorbisfile to VC2012 solution
audio: Add Ogg Vorbis support to playWave3D()

Now you can use Ogg Vorbis sound effect as argument to playWave3D(),
but the source must be monoral.
Add flying sound effect to Sceptor

There are two sound source files to make difference between high and
low throttle.  Adjusting sound volume is not enough to simulate power
variance, because the distance between the listener and the sound
source can affect volume, too.  Adjusting blending factor of high and
low frequency makes difference to the listener.
surface: Remove unnecessary include files in Apache.cpp
surface: Add chaingun shoot sound to Apache
surface: Add Apache's rotor sound as looping sound