Implement startListening

[esgraham]

• The startListening functionality was added to Android
• The RecognizefromMicrophone function was renamed to startListening in iOS
• The SetSubscription method was renamed init.
• The other methods were changed in the javascript file to use camelCase.
• The plugin is using a single callback object for the recognizing and recognized events for both iOS and Android.
• The callback schema includes an 'isFinal' boolean value and a 'result' string
• Update relevant documentation

Issue #9