Prints all primes smaller or equal to a limit n
Efficient of when n <= 10,000,000
Algorithm
- Assume all numbers from 2tonare unmarked 
- Mark the number 2 as prime, then mark all multiples of 2 as composite
 
- The next unmarked number from 2 is prime (3 in this case), then mark all multiples of 3 that are currently unmarked as composite
 
- Repeat the process with all subsequent unmarked numbers
