move sources to src
reformat code
remove comments. reformat description
extract class PrimeCounter
extract validateParameters

use IllegalArgumentException instead of System.exit(0).
extract calculatePrimes

rename calculatePrimes to getPrimesForRange and extract the calculation
logic from that. getPrimesForRange also returns List instead of void.
extract isNotDividable from isPrime
inline parameters
make PrimeCounter static
re-organize and reformat code
add test class for PrimeCounter