add inspiration resources.

hs/DataStructures.hs

{-|
    Module: DataStructures
    Description: Having fun with (functional) data structures
    Inspired by:
      * Purely Functional Data Structures, by Chris Okasaki
      * <http://www.infoq.com/presentations/Functional-Data-Structures-in-Scala Functional Data Structures in Scala>, by Daniel Spiewak
-}
module DataStructures where
import Prelude hiding (concat, drop, last, length, reverse, take)