Implement toString() for Color class

Author: TBlueF

src/main/java/de/bluecolored/bluemap/api/math/Color.java

@@ -167,4 +167,13 @@ public int hashCode() {
         return result;
     }
 
+    @Override
+    public String toString() {
+        return "Color{" +
+                "r=" + r +
+                ", g=" + g +
+                ", b=" + b +
+                ", a=" + a +
+                '}';
+    }
 }