Create a function to get the rank, user id and points of all the users

Hey Paul,

Seeing you're interesting in fleshing out the API first I'll add this function for your consideration.

I added https://github.com/BronsonQuick/achievements/commit/dad89f8b8752aa7fd1318771f8633210c4e6bf01#L0R370 to make sure that null values were pushed to the bottom of the stack.

Sorry for the delay. Life and clients have been getting in the way of my coding lately!

Cheers!