Update to 1.840
    
    - New upstream release 1.840
      New Features
      - Added MCE::Mutex::Channel2 providing two locks using a single channel; the
        secondary lock is accessible by calling methods with the '2' suffix, e.g.
        primary mutex ->lock, ->unlock; secondary mutex ->lock2, ->unlock2
      - Added MCE::Channel providing queue-like and two-way communication
        supporting threads and processes
      - Added MCE::Child and compatibility with Perl 5.8; MCE::Child is based on
        MCE::Hobo, but using MCE::Channel for data retrieval without involving a
        shared-manager process
      - Added MCE::Channel examples { channel1.pl and channel2.pl } using threads
        and MCE::Child respectively
      Enhancements
      - IPC update; removed unnecessary overhead including private methods _sysseek
        and _syswrite from MCE::Util (no longer needed)
      - Improved MCE->do, now callable by workers and the manager process
      - Updated MCE::{ Flow, Grep, Loop, Map, Step, and Stream } documentation on
        passing an array reference versus a list for deeply input data
      - Updated and re-organized the top-level MCE documentation, particularly
        improved clarity for the 'MCE Models' section
      - Removed MANIFEST.SKIP
      - Update MCE::Channel POD documentation