Raindrops: Updated to use functions. Example now uses anonymous function

I decided to structure the exercise in a similar manner to the python implementation. I also decided to use an anonymous function in the example to show how to use them.

I'm starting to get more comfortable with branches.
I just realized here we could do 

    $ret = $pling ? 'Pling' : '';

and then remove line 18. Can't do it right this second.