Improvements on documentation (#340)

* Improvements on documentation and some refactor

* ts | js -> typescript (docs)

src/plugins/plugin.ts

@@ -1,10 +1,10 @@
 import { get } from '../util';
+import { Observable } from 'rxjs/Observable';
 
 declare var window;
 declare var Promise;
 declare var $q;
 
-import {Observable} from 'rxjs/Observable';
 
 /**
  * @private
@@ -230,7 +230,7 @@ export const wrap = function(pluginObj: any, methodName: string, opts: any = {})
  * Class decorator specifying Plugin metadata. Required for all plugins.
  *
  * @usage
- * ```ts
+ * ```typescript
  * @Plugin({
  *  name: 'MyPlugin',
  *  plugin: 'cordova-plugin-myplugin',