PollDance
---------
Date: January 28th, 2013
Authors: Justin Karneges <justin@fanout.io>
         Katsuyuki Ohmuro <harmony7@pex2.jp>

PollDance is a general purpose AJAX library, implementing multiple transports
to ensure cross-domain access works in all major browsers. It also provides
conveniences for long-polling applications such as retries, exponential
backoff between requests, and randomized request delaying.

Dependencies:

  json2.js

Available Transports:

  XmlHttpRequest - for all modern CORS browsers
  JSON-P - for IE7, IE8, IE9, and older versions of other browsers

Limitations:

  - Responses from the server must be in JSON format. This library will parse
    the data and return an object to the application.
  - If the JSON-P transport is used, the request headers and body are subject
    to URI length limitations of the browser and server.
  - It is not possible to inspect the headers of a response.

Usage:

  var req = new PollDance.Request();
  req.on('finished', function(code, result) { ... });
  req.on('error', function(reason) { ... });
  var headers = { ... };
  var body = 'some data';
  req.start('POST', 'http://example.com/path', headers, body);

JSON-P Protocol:

  This library supports JSON-P by supplying the following query string
  parameters in the request:

  callback: the JavaScript function to call in the response
  method: the method name (default GET)
  headers: additional headers encoded as JSON (default none)
  body: request body (default empty)

  This protocol dictates that the presence of the "callback" parameter
  signifies the request as a JSON-P request. The remaining parameters are
  optional.

  The server is expected to reply with a JSON object of the form:

    {
      "status": code,
      "value": object
    }