Introduce cmake (min 2.8.12) to StepMania.

tl-dr: view the Build directory to see.

This is intended to replace the project files that we presently maintain
so that only a single set is needed instead of multiples.

The following setups were used for testing:

* Windows 8 and Visual Studio 2013 Desktop Express
* Windows 7 and Visual Studio 2012
* Mac OS X Mavericks and Xcode
* Ubuntu and makefiles
* Fedora 21 and makefiles

All three operating systems can generate projects, compile, link, and
run. Windows and Mac OS X users will find their compiled binary in the
same location as before, but Linux users will be surprised: it goes
straight into the root directory, along with a symlinked GtkModules.so
as appropriate. There is no more need for a manual symlinking step.

Known issues:

* At this time, MinGW likely does not work. Extra time will be needed.
* The WITH_JPEG option may go away, and we'll just always require it.
* Some linux libraries can use the system equivalents, but that is not up yet.

For more information, check out the Build directory.

src/global.cpp

@@ -8,6 +8,8 @@
 #  endif
 #elif defined(MACOSX)
 #  include "archutils/Darwin/Crash.h"
+#  include <stdlib.h>
+#  include <unistd.h>
 using CrashHandler::IsDebuggerPresent;
 using CrashHandler::DebugBreak;
 #else