Fix missing sdl3game.pc for pkg-config, change sprite speed and character movement values to long int expressed in nanoseconds for better compatibility with SDL_Time and locking against game clock, still expressed as milliseconds in json

include/sdl3game/sprite.h

@@ -29,7 +29,7 @@ typedef struct {
   int frames; // how many frames are in this animation
   int width;
   int height;
-  int speed; // how many milliseconds a given sprite frame should be visible before cycling
+  long int speed; // how many milliseconds a given sprite frame should be visible before cycling
   bool loop; // when this sprite is done playing, it should immediately start again
   bool loopReverse; // when this sprite is done playing, it should go in reverse order through its frames
   char name[SPRITE_MAX_NAME_LENGTH];