Create Ajax.ts

This file has dependencies
 - Encoding.ts
 - Http.ts (optional)

Handles AJAX requests
Project: https://github.com/Steve-Fenton/TypeScriptUtilities
Author: Steve Fenton

Example usage:

var ajaxOkayCallback = function (response: Ajax.IAjaxResponse): void { 
  alert(response.responseText);
};

var ajaxProblemCallback = function (response: Ajax.IAjaxResponse): void { 
  alert('Failed');
};

var ajaxRequest = new Ajax.Request(Http.HttpVerb.GET, '/MyUrl/');
ajaxRequest.addHttpStatusCallback([200, 201], ajaxOkayCallback);
ajaxRequest.addDefaultCallback(ajaxProblemCallback);
ajaxRequest.run();