Fix to get $screenname before $count.

Backwards compatibility is a decent reason to not flip these around, but if done safely I think it's worth doing just to save on head pain.

Screen names are almost certainly never going to be passed in as integers, even if someone had a crazy integer screen name, the likely-hood is that it would be a string, this should allow for the first two parameters to be passed in in any order and gracefully handled.

If someone passes a count in as the first argument and as a string, I'd say they deserve the effects.

:)
Updated recommended syntax in README examples.
Merge pull request #1 from stevelacey/patch-1

Fix to get $screenname before $count.