Add 'exa: ' before all command-line errors

src/main.rs

@@ -93,7 +93,7 @@ fn main() {
         }
 
         OptionsResult::InvalidOptions(error) => {
-            eprintln!("{}", error);
+            eprintln!("exa: {}", error);
 
             if let Some(s) = error.suggestion() {
                 eprintln!("{}", s);

xtests/help.toml

@@ -4,4 +4,4 @@ shell = "exa --help"
 stdout = { file = "outputs/help.ansitxt" }
 stderr = { empty = true }
 status = 0
-tags = [ 'help ']
+tags = [ 'help' ]