v2.1.0. Improvement.

- v2.1.0 August 19, 2013
	- will now always return `null` for consistency
		- as return values are only possible with synchronous methods
	- will now ignore returned errors on asynchronous functions
		- asynchronous errors must now give the error via the completion
callback
		- this is to avoid the possibility of the completion callback being
called twice (once for the returned error via ambi, once via your
application)
	- will now ignore thown errors
		- this was determined to be outside the scope of ambi, if you want
this functionality use the more full featured [taskgroup
package](http://npmjs.org/package/taskgroup)