Improve sieve of Eratosthenes

[MaximSmolskiy]

Sieve of Eratosthenes is quite efficient nearly linear algorithm. But current implementation is naive quadratic brute force.

Before:

>> tic; sieveER(100); toc;
Elapsed time is 0.0519161 seconds.
>> tic; sieveER(1000); toc;
Elapsed time is 5.05789 seconds.

After:

>> tic; sieveER(100); toc;
Elapsed time is 0.00150514 seconds.
>> tic; sieveER(1000); toc;
Elapsed time is 0.00985217 seconds.

[cozek]

Thanks!