aded junit-benchmarks dependency
refactored AbstractSieve benchmark test to use junit-benchmarks AbstractBenchmark

SieveTest is now SieveBenchmarkTest. benchmarks the four sieve
implementations using junit-benchmarks, for n=50000 (temporarily).
Rot13: create StringBuilder with expected string size
Rot13: in-place char[] replacement, plus benchmark test

ROT13 algorithm now does in place char[] replacement