Fix race condition with response attribute. Fixes #12.

There are two use cases as I see it. One is to fire off a series of requests
and react to all of them. The other is to treat all responses but the response to the most recent request as stale (e.g. in a search app you only want to show results for the current search and ignore out of order responses)

This change accomodates both use cases by firing events for every response (
which is unchanged), but setting up the response attribute to be either the
response for the most resent request, or null. Likewise it exposes an error
attribute that behaves the same way.
Add support for HTTP PATCH method
move tests from core-tests
Merge branch 'master' of https://github.com/Polymer/core-ajax
add a demo page to show off the race condition behavior
make demo-avoid-race-condition a test instead
Merge pull request #14 from rictic/master

Fix race condition with response attribute. Fixes #12.
Add progress and loading attributes; includes docs, demo, and test.
update to webcomponents.js
Fixes #36
Address comments; improve reliability of progress test.

 * changed single-quoted attributes to double quoted
 * use a slower network request to more reliably assert about the request
   while it is loading
 * add a core-range to the progress test in order to catch the assignment to
   read-only property bug
minor: set progress to null on the prototype
minor: document the progressProxy object
Merge pull request #27 from rictic/progress

Add progress and loading attributes; includes docs, demo, and test.
Automatically send requests on body change.
Change deprecated platform.js to webcomponents.js
Merge pull request #38 from TomBrouws/master

Change deprecated platform.js to webcomponents.js
Update core-ajax docs to reflect new auto behavior
Merge pull request #39 from garlicnation/master

Extend auto's behavior to send requests on body change.
Merge pull request #18 from Wenqer/patch-1

Add support for HTTP PATCH method.