Add typings and tests for 'direction' option

types/easymde-test.ts

@@ -202,3 +202,11 @@ new EasyMDE({
         'link',
     ],
 });
+
+new EasyMDE({
+    direction: 'ltr',
+})
+
+new EasyMDE({
+    direction: 'rtl',
+})

types/easymde.d.ts

@@ -222,6 +222,8 @@ declare namespace EasyMDE {
         syncSideBySidePreviewScroll?: boolean;
 
         overlayMode?: OverlayModeOptions;
+
+        direction?: 'ltr' | 'rtl';
     }
 }