Move error summary output to stdout (#87)

Modifies the summary printed at the end to be entirely in stdout
instead of mixed between stderr and stdout. Without this commit,
suppressing stdout output or capturing stderr output for logs would
result in "The following links could not be resolved:" being printed
without the list of broken links (which should be the same as the stderr
output.)

src/lib.rs

@@ -329,8 +329,8 @@ pub async fn run(config: &Config) -> Result<(), ()> {
     if errors.is_empty() {
         Ok(())
     } else {
-        eprintln!();
-        eprintln!("The following links could not be resolved:");
+        println!();
+        println!("The following links could not be resolved:");
         println!();
         for res in errors {
             for link in &link_target_groups[&res.target] {