feature: makes "compile" exercise print output, resolves #270

When running "compile"-mode exercises in interactive `verify` mode,
we print their output when we prompt the learner if they want to
continue. This improves the "experimentation" experience, since
trying different things does produce a visible change.

tests/integration_tests.rs

@@ -31,7 +31,7 @@ fn verify_all_success() {
 }
 
 #[test]
-fn verify_all_failure() {
+fn verify_fails_if_some_fails() {
     Command::cargo_bin("rustlings")
         .unwrap()
         .arg("v")