EquaSets Cleanup

-Changed find to return Option[T].
-Added scaladocs to map, flatMap, filter and foreach methods of EquaSet/SortedEquaSet.. 
-Added initial implementation for withFilter method in EquaSet.
-Added Scaladoc for into. 
-Fixed the Scaladoc on repr. 
-Added Scaladoc for size. 
-Changed EquaSet's isTraversableAgain to always return true, unless overriden.
-Changed a `EquaSet` to an `EquaSet`, and updated transpose method scaladoc.