Add possibility to play with focal length and aperture to the camera. Not enabled by default.

source/math_helper.cpp

@@ -68,4 +68,9 @@ double max3(double a, double b, double c)
 double frand()
 {
     return rand() / ((double) RAND_MAX);
+}
+
+double frandclip(double min, double max)
+{
+    return (frand() * (max - min)) + min;
 }