jQuery.ajax: `success` callback and `dataFilter` signatures should use Anything type

_(This was discussed on [another issue](/jquery/api.jquery.com/issues/490#issuecomment-42877855) and recommended to be reported separately.)_

The signature for the `success` callback of [`jQuery.ajax`](//api.jquery.com/jquery.ajax/#jQuery-ajax-settings) is misleading in that it denotes that the function will be passed a `PlainObject` as its first argument, even though it is later (and more accurately) noted that the passed argument is "formatted according to the `dataType` parameter." Indeed, the `data` can even potentially be of _any_ type if one uses custom `converters`. The same issue exists for the `dataFilter` setting's function signature.

These signatures should probably use `Anything` in place of `[Plain]Object`.