Edit Platform.h to enable compilation with MS Visual Studio 2012.
Remove unnecessary compiler checks

We should strive for standard c++ and in cases where compiler extensions
are useful, use feature checks instead of hard-coding supporting
compilers.

Compiler names and versions are still useful in error reports, but
have been moved out of Platform.h into a separate Compiler.h.
Tweak AUTHORS file, add "MANY THANKS TO" section
Remove hard-coded credits text from Menu.cpp

Instead, read the AUTHORS file at compile time.
Once we ship our own resources, the credits can be read at run-rime.