Allow left/right for collapse, more hotkeys

* Use 'b' to toggle fold icon before/after key
* Use 'g' to toggle indentation guide lines
* Cosmetic fixes

src/Editor/Menu.php

@@ -39,7 +39,7 @@ class Menu
 
         [$w,$h] = $this->terminal->getSize();
         if ($height == 0) {
-            $height = min($h - 5, count($this->items) + 4);
+            $height = min($h - 5, count($this->items) + 2);
         }
         if ($left == 0) {
             $left = round(($w - $width) / 2);