Add ol.easing to api docs

Similar to #2125.

I think the individual functions should be documented, even if only to say they are a reference to the goog function. This is not an area I know much about; would someone like to give me a one-line description for each one and I'll add?

I think github prefer not to have raw links, so I changed the Raphael links to the repo.

PS I regenerated the apidocs and AFAICS the links all seem to be correct.