Moved the SDL version back to SDL_version.h

Added a comment at the top of SDL.h with the current version, for informational purposes

include/SDL3/SDL_version.h

@@ -37,6 +37,13 @@
 extern "C" {
 #endif
 
+/**
+ * The current version of SDL
+ */
+#define SDL_MAJOR_VERSION   3
+#define SDL_MINOR_VERSION   1
+#define SDL_MICRO_VERSION   2
+
 /**
  * This macro turns the version numbers into a numeric value.
  *