utils: add a simple function to substract a variable to another to zero

gamecore/utils/math.lua

@@ -40,6 +40,16 @@ function Math.round(num)
   return math.floor(num + 0.5)
 end
 
+function Math.toZero(num, sub)
+  local sub = math.floor(sub)
+
+  if math.abs(num) < sub then
+    return 0
+  else
+    return num - (sub * Math.sign(num))
+  end
+end
+
 -- VECTOR/DIRECTION functions
 -- Easy-to-use function to handle point and motion