refactor(meta-command): have execute be a member function

src/meta_commands.rs

@@ -2,6 +2,18 @@ pub enum MetaCommand {
     Exit,
 }
 
+pub struct MetaCommandExecuteResult {
+    pub should_exit: bool,
+}
+
+impl MetaCommand {
+    pub fn execute(&self) -> MetaCommandExecuteResult {
+        match self {
+            MetaCommand::Exit => MetaCommandExecuteResult { should_exit: true },
+        }
+    }
+}
+
 pub enum MetaCommandParseError {
     Unrecognized { cmd: String },
 }