Added `delayed` example to README
delayed option bugfix: prevents from running the first time when condition is false
Passing the xhr object along with the error event

Fixes #17
0.2.5 Minor Release

  - Added validation before fetching as well as before deferring
  - Test Cases
  - Bumped version to 0.2.5

Fixes #18
Merge branch 'master' into gh-pages

Conflicts:
	backbone.poller.js
	backbone.poller.min.js
Updated Docs