feat: send polls (#2377)

* feat: added Poll class

* feat: logic for sending polls added

* updated poll properties on returned message instance

* docs updated

* usage example updated

* module fixed

* 'pollSendOptions' changed to 'options'

* window.compareWwebVersions fixed

* small update to improve the performance of findImpl fix

* added option for custom message secret

* usage example updated

src/structures/index.js

@@ -19,4 +19,5 @@ module.exports = {
     List: require('./List'),
     Payment: require('./Payment'),
     Reaction: require('./Reaction'),
+    Poll: require('./Poll'),
 };