add SSE4.2 optimized hash function

add SSE4.2 optimized hash function

For systems supporting SSE4.2, use the crc32 instruction as a fast
hash function. Also, provide a better fallback hash.

For both new hash functions, we hash 4 bytes, instead of 3, for certain
levels. This shortens the hash chains, and also improves the quality
of each hash entry.