Please don't deprecate the RSAA constant

In https://github.com/agraboso/redux-api-middleware/blob/master/src/RSAA.js#L6 you have deprecated the RSAA constant, however it's essential to be able to access that in the case where a `payload` function accepts the `rsaa action` and you need to deconstruct it to get (in my case) access to the `meta` field supplied to the action.

Please consider not deprecating this.