cam: extend frustum's far distance helper (#71)

* this will help to implement zoom easily

include/cglm/call/cam.h

@@ -61,6 +61,10 @@ glmc_perspective(float fovy,
                  float farVal,
                  mat4 dest);
 
+CGLM_EXPORT
+void
+glmc_persp_move_far(mat4 proj, float deltaFar);
+
 CGLM_EXPORT
 void
 glmc_perspective_default(float aspect, mat4 dest);