code: function(key) {
  			var idx;
  			do {
  				idx = this.contents.indexOf(key, idx);
  			} while(idx !== -1 && !isEven(idx));
  			return idx;
  		}
docs: Get an index of a key. Because we store boths keys and values in
  a flat array, we ensure we are getting a key by checking that it is an
  even number index (all keys are even number indexed).