A new date format "--date=human" that morphs its output depending
on how far the time is from the current time has been introduced.
"--date=auto" can be used to use this new format when the output is
going to the pager or to the terminal and otherwise the default
format.

* lt/date-human:
  Add `human` date format tests.
  Add `human` format to test-tool
  Add 'human' date format documentation
  Replace the proposed 'auto' mode with 'auto:'
  Add 'human' date format