add diffy, prettydiff

diffy/src/main.rs

@@ -0,0 +1,16 @@
+use diffy::PatchFormatter;
+
+const A: &str = r##"
+hello world
+hatter
+"##;
+const B: &str = r##"
+hello world
+hatterj
+"##;
+
+fn main() {
+    let patch = diffy::create_patch(A, B);
+    let f = PatchFormatter::new().with_color();
+    print!("{}", f.fmt_patch(&patch));
+}