v1.4.0

• Change default MRC format version from 20140 to 20141 and update validation
  to allow files with both format numbers as valid.
• Add mrcfile.read() and mrcfile.write() functions for quick one-off accesses
  to the MRC data array without needing to keep an MrcFile object open (thanks
  to Alister Burt).
• Allow the extended header to be set when creating a file with
  mrcfile.new_mmap() (thanks to James Parkhurst).
• Add file size checks to avoid allocating huge amounts of memory when opening
  corrupt or non-MRC files in permissive mode.
• Update numpy and Python version compatibility to drop support for Python
  3.4 and 3.5 and numpy < 1.16, and add support for numpy 1.21 and 1.22.
• Fix bug intepreting FEI extended headers on big-endian hardware.
• Documentation updates.