Add support for > and >> prompts with new readline

luprex/cpp/drv/readline.cpp

@@ -117,6 +117,11 @@ void ReadlineDevice::set_print_callback(print_callback cb) {
     print_cb_ = cb;
 }
 
+void ReadlineDevice::set_prompt(const CodepointString &prompt) {
+    desired_prompt_ = prompt;
+    echo_command();
+}
+
 void ReadlineDevice::erase_command() {
     int ccsize = current_prompt_.size() + current_command_.size();
     if (ccsize > 0) {
@@ -168,6 +173,7 @@ CodepointString ReadlineDevice::putcode(char32_t c) {
         desired_command_.clear();
         current_prompt_.clear();
         current_command_.clear();
+        echo_command();
         return result;
     } else if ((c == '\b') || (c == 127)) {
         int len = desired_command_.size();