[WIP] Speedup sync

[elbandi]

Go routine in Sync method reads the file byte-to-byte in rolling mode. thats very slow. I rewrite the whole func to a different solution: it reads block (current 16) to memory, and do the rolling search in that data. if not enough data in buffer, it copy the remaining data to the begin, and fill the buffer again. (Block size is configurable)

This PR is just a work-in-progress pull, no need to merge. Any suggestions or ideas are welcome. :)