Add a silent mode for running the diff.

src/bin_compare.rs

@@ -34,10 +34,17 @@ fn main_body() -> Result<(), Box<dyn std::error::Error>> {
     let args = std::env::args().skip(1);
     if args.is_empty() {
         let org_contents = read_stdin_to_string()?;
-        run_anonymous_compare(org_contents)
+        if let Ok(true) = run_anonymous_compare(org_contents) {
+        } else {
+            Err("Diff results do not match.")?;
+        }
+        Ok(())
     } else {
         for arg in args {
-            run_compare_on_file(arg)?
+            if run_compare_on_file(arg)? {
+            } else {
+                Err("Diff results do not match.")?;
+            }
         }
         Ok(())
     }