Added FixedSizeSetBucket and SetBucket

+ FixedSizeSetBucket
+ SetBucket
+ FixedSizeHashBucket.KeyComparer
+ HashBucket.KeyComparer
! fixed documentation wording in FixedSizeHashBucket
! renamed FixedSizeHashBucket.Vaues to FixedSizeHashBucket.Pairs
! renamed HashBucket.Vaues to HashBucket.Pairs