Review libc dependencies and remove when possible

Just for clarification, no plans to remove libc dependency, just did some code analysis to see how much raylib depend on stardard C library. My conclusions:

 - stdlib.h: primary dependency is for malloc() and free()
 - stdio.h: primary dependency is for FILE access, maybe it could go through a custom ABI?
 - string.h: just around 8 functions required
 - math.h: just around 8 functions required
 - others: 1-2 functions required for some other headers

src/camera.h

@@ -133,7 +133,7 @@ void SetCameraMoveControls(int frontKey, int backKey,
 
 #if defined(CAMERA_IMPLEMENTATION)
 
-#include <math.h>               // Required for: sqrt(), sinf(), cosf()
+#include <math.h>               // Required for: sinf(), cosf(), sqrtf()
 
 #ifndef PI
     #define PI 3.14159265358979323846