handle NaN in images

src/image.rs

@@ -7,6 +7,7 @@ impl From<String> for Image {
     #[inline]
     fn from(string: String) -> Image {
         let string = string.replace("\n", "");
+        let string = string.replace("NaN", "0");
         let pixels: Vec<&str> = string.split("").collect();
         // the above seems to add an extra "" at the start and end of the vec, so strip them below
         let pixels = &pixels[1..(pixels.len() - 1)];