D3 used to support Aureal 3-Dimensional sound cards, providing 3D spatial audio. The hardware and drivers is outdated, so all support in code has been removed, including UI mixer setting.
Read more about A3D here: https://en.wikipedia.org/wiki/Aureal_Semiconductor#A3D
Join the license header with historical comments using a separator so IDEs can correctly parse the initial header.
Also use .gitattributes to ensure all files are LF.
This is all in unused/unnecessary/leftover code, but the code wouldn't
build without Xlib headers on the system, which was forcing the Mac builds
to install xquartz.
This also removes renderer/SoftwareOpenGL*, which was _not_ a
software-rendered OpenGL, but just an older version of the same code that's
in HardwareOpenGL.cpp--old enough to still talk to glX directly, which is
what caught my attention.
The vast majority of this is fixing up `char *` that should be `const char *`
but a handful of other fixes, like potential buffer overflows that GCC
noticed, etc, were applied as well.
This removes `-Wno-write-strings` from CMakeLists.txt, as it is no longer
necessary, as there is no longer a flood of compiler warning spam when
building.
This does not fix all compiler warnings; there are still a handful, and they
are legitimate, but they can be dealt with in a future commit.
