Update to 1.818
    
    - New upstream release 1.818
      - Updated bin/mce_grep for determining chunk level and chunk size
      - Fixed an issue for not seeing STDERR output with '--chunk-level=file'
      - Added support for zgrep, zegrep, and zfgrep
      - Replaced Sereal with Sereal::Decoder and Sereal::Encoder in Makefile,
        inside recommends section; ditto for META files
      - Refactored MCE::Queue: merged local and manager code base into one
      - Removed t/04_norm_que_local.t and t/04_prio_que_local.t
      - Added 'end' method to MCE::Queue
      - Updated documentation on dequeue and pending
    - Add symlinks for mce_grep variants