fix(clap): print usage if command is missing

Also, fixed config-dir substitution in flag's help message

src/mako/cli/lib/argparse.mako

@@ -104,7 +104,7 @@ Configuration:
         CONFIG_DIR_FLAG,
         "A directory into which we will store our persistent data. Defaults to "
         "a user-writable directory that we will create during the first invocation."
-        "[default: ${CONFIG_DIR}]",
+        "[default: %s" % CONFIG_DIR,
         'folder',
     ))
 

src/mako/cli/lib/engine.mako

@@ -69,12 +69,14 @@ impl<'n, 'a> Engine<'n, 'a> {
                     % endfor # each method
                     _ => {
                         err.issues.push(CLIError::MissingMethodError("${mangle_subcommand(resource)}".to_string()));
+                        writeln!(io::stderr(), "{}\n", opt.usage()).ok();
                     }
                 }
             },
 % endfor # each resource
             _ => {
                 err.issues.push(CLIError::MissingCommandError);
+                writeln!(io::stderr(), "{}\n", ${SOPT}.usage()).ok();
             }
         }
 

src/rust/cli/cmn.rs

@@ -351,7 +351,7 @@ impl fmt::Display for CLIError {
                 writeln!(f, "'{}' does not match {}pattern <key>=<value>", kv, hashmap_info)
             },
             CLIError::MissingCommandError => writeln!(f, "Please specify the main sub-command"),
-            CLIError::MissingMethodError(ref cmd) => writeln!(f, "Please specify the method to call on the {} command", cmd),
+            CLIError::MissingMethodError(ref cmd) => writeln!(f, "Please specify the method to call on the '{}' command", cmd),
         }
     }
 }