Matches now use memcpy and memset when possible.

Block loops have been rewritten to be more optimizer friendly.

Reworks Symbol and HuffmanDecoder
* Symbol now only includes the value and number of code bits.
  decodeSymbol returns only the value.
* HuffmanDecoder now takes the regular bits instead of the reversed.
* Code table construction now uses buckets instead of sorting.
* For linked codes, the value field of Symbol is now used as the next
  index. The actual value is the element index.
* InvalidCode is now detected only once with a special linked index.

Performance is 39.7% faster than before and 1.1% faster than gzip using
a sample created from compressing a tar of the src directory.