Bit error correction code improved

Hi,

I added some code to run the bit error correction based on a small table. This gives a speedup of roughly 30-40 resp. around 80 for 1-bit resp. 2-bit errors. Thus, the code can now be run without an exceptionally fast cpu or burning many cycles...

Some background: mathematically, the crc is linear in the bit error vector, i.e. crc(m^e) = crc(m)^crc(e), where m is the message and e is the error bit vector.

A note of caution: this code works directly for the crc computation method in your code, which is changed in a special way w/ regard to the original code by antirez. For porting back, some work is needed.

Best regards,
Ulrich