implemented getStats method
implemented append for String
implemented append method for IDnaStrand
implemented reverse method
implemented toString method so testing reverse() will work
LinkStrand implementation passes 4/7 tests: size, toString, append, and doubleAppend
LinkStrand implementation now passes initialize(), 5/7 total
LinkStrand implementation now passes reverse(), 6/7 total
LinkStrand implementation now passes cutAndSplice(), passes all tests