support creating a namespace by letting the user type in a namespace. In the future while I replace dialouger I'll have a typeahead-style selection widget to let me unify these two functions

src/main.rs

@@ -181,11 +181,28 @@ fn change_namespace(db_conn: &mut db::DbHandle, master_key: [u8; 32]) -> String
     namespaces[selection].name.to_owned()
 }
 
+fn create_namespace(db_conn: &mut db::DbHandle, master_key: [u8; 32]) -> String {
+    let namespace: String = Input::with_theme(&ColorfulTheme::default())
+        .with_prompt("Namespace")
+        .default("main".to_owned())
+        .interact()
+        .unwrap();
+    namespace
+}
+
 fn shell(db_conn: &mut db::DbHandle, master_key: [u8; 32], _namespace: &str) {
     let mut namespace: String = _namespace.to_owned();
 
     loop {
-        let selections = &["get", "list", "set", "generate", "change namespace", "exit"];
+        let selections = &[
+            "get",
+            "list",
+            "set",
+            "generate",
+            "change namespace",
+            "create namespace",
+            "exit",
+        ];
         let main_menu_prompt = format!("Main Menu ({})", namespace);
 
         let selection = Select::with_theme(&ColorfulTheme::default())
@@ -202,6 +219,9 @@ fn shell(db_conn: &mut db::DbHandle, master_key: [u8; 32], _namespace: &str) {
             "change namespace" => {
                 namespace = change_namespace(db_conn, master_key);
             }
+            "create namespace" => {
+                namespace = create_namespace(db_conn, master_key);
+            }
             "exit" => break,
             _ => panic!("Unrecognized command"),
         };