Update sinon spy api documentation

[ckwong90]

I was looking a way to spy on an objects setter and getter function and noticed that it's not in the docs http://sinonjs.org/releases/v2.0.0-pre.6/spies, but the api is burried in an issue #917.

Add api docs for

sinon.spy(object, "method", ["type"]);  //Where type is either "setter" or "getter"

[fatso83]

That is because we are reworking the API for that, and that it is currently undergoing a change. It is currently not possible with the release candidate. See #1297 for background info.

[fatso83]

This is now on http://sinonjs.org/releases/v2.0.0/stubs/. See get and set methods.