Error property support #52

I have become a little more familiar with the API's, and I really like them, they are super flexible and encourage use of FSA which is great.

I have been able to create an error action using createStandardAction but it wasn't clear how to do it with the other 2 API's.

The way our action creators were written previously, the meta value was the first parameter - so we would like to continue that, so we are writing them using action, but looking at action it isn't clear how to add the error: true property for an error action. (Actually now we are using createAction because we want getType)

Maybe action could be extended to have a 3rd parameter that just let you mix in whatever properties you wanted - or perhaps less flexible but better for FSA's would be to have an error parameter that let you set that property.

   fetchDataError: (widgetKey: string, error: Error) =>
        createStandardAction(FETCH_DATA_FAILURE).map((payload: Error, meta: string) => ({
            payload,
            meta: { widgetKey: meta },
            error: true as true
        }))(error, widgetKey)

Using the API in this way though breaks getType

I haven't tried the Async API's yet though. They might be useful here, but i still need the parameter ordering.