def merge(arr)
      super(arr.inject({}) {|s,x| s[x] = true; s })
    end
def merge(arr)
      super(arr.inject({}) {|s,x| s[x] = true; s })
    end
Merge _arr_ with receiver, producing the union of receiver & _arr_

   s = Extlib::SimpleSet.new([:a, :b, :c])
   s.merge([:c, :d, :e, f])  #=> #<SimpleSet: {:e, :c, :f, :a, :d, :b}>

 @param [Array] arr Values to merge with set.

 @return [SimpleSet] The set after the Array was merged in.

 @api public