Add contour tracing example

examples/contours.rs

@@ -0,0 +1,33 @@
+mod common;
+
+use ccvl::*;
+
+const OUTER: image::SRGBA = image::SRGBA {
+    r: 0.0,
+    g: 1.0,
+    b: 0.0,
+    a: 1.0,
+};
+const INNER: image::SRGBA = image::SRGBA {
+    r: 0.0,
+    g: 0.0,
+    b: 1.0,
+    a: 1.0,
+};
+
+fn main() -> std::process::ExitCode {
+    common::process_image(|mut img| {
+        let greyscale = img.map(|p| image::Luminance::from(p));
+		let thresholded = filter::threshold_auto(greyscale);
+        let contours = contour::find(thresholded);
+        for contour in contours {
+            for (x, y) in contour.trace {
+                *img.at_mut(x, y) = match contour.kind {
+                    contour::Kind::Inner => INNER,
+                    contour::Kind::Outer => OUTER,
+                };
+            }
+        }
+        img
+    })
+}