Add duplicate (^D), basic search, bugfixes

* Use ^D to duplicate array items
* Use / to search, matching keys will be highlighted
* Don't attempt to load non-existing files when passed on command line

src/entry.php

@@ -58,7 +58,7 @@ $terminal = new NoccyLabs\JsonEdit\Terminal\Terminal();
 Settings::load(SETTINGS_FILE);
 
 $editor = new NoccyLabs\JsonEdit\Editor\Editor($terminal);
-if ($filename) {
+if ($filename && file_exists($filename)) {
     $editor->loadFile($filename);
 } else {
     $editor->loadDocument((object)[]);