feature-CMAKE_MESSAGE_CONTEXT
-----------------------------

* The :variable:`CMAKE_MESSAGE_LOG_LEVEL` variable can now be used
  to persist a log level between CMake runs, unlike the ``--log-level``
  command line option which only applies to that particular run.

* The :command:`message` command learned to output context provided in
  the :variable:`CMAKE_MESSAGE_CONTEXT` variable for log levels
  ``NOTICE`` and below.  Enable this output with the new ``--log-context``
  command-line option or :variable:`CMAKE_MESSAGE_CONTEXT_SHOW` variable.