Adds documentations for adapters and main constructors (#4951)

* wip

* Adds documentations for adapters, and constructors

* nits

* nit

src/Adapters/Push/PushAdapter.js

@@ -11,7 +11,19 @@
 // Default is ParsePushAdapter, which uses GCM for
 // android push and APNS for ios push.
 
+/**
+ * @module Adapters
+ */
+/**
+ * @interface PushAdapter
+ */
 export class PushAdapter {
+  /**
+   * @param {any} body
+   * @param {Parse.Installation[]} installations
+   * @param {any} pushStatus
+   * @returns {Promise}
+   */
   send(body: any, installations: any[], pushStatus: any): ?Promise<*> {}
 
   /**