Commands to add
===============

Commands that change arrays:

layer
-m|--mode=min|max|median|or|and|xor|diff|add|xadd|sub|xsub|mul|div file...

Commands that change streams:

stream-merge [unnecessary; simply use cat]
stream-split 
stream-extract (select)
stream-foreach
stream-reverse


Other things
============

- Man page, texinfo manual.
  These just need to give a short description and then mention
  'gtatool help' and 'gtatool help <cmd>'.

- Add a test for every command. The test infrastructure is already finished,
  including automatic use of valgrind if available.
