More CLI improvements, adding a 'define' subcommand for adding new Event Definitions.
More CLI improvements, adding a 'define' subcommand for adding new
Event Definitions.

* recurrence-cli
  (_date_re): New.
  (RecurrenceCommandLine.prompt): Was confirm().  Now accepts a
    validator callback function argument, and tries to be a bit more
    generic than a simple yes/no question now.
  (RecurrenceCommandLine.datestr_to_datetuple): New.
  (RecurrenceCommandLine.cmd_define): New subcommand implementation.
  (RecurrenceCommandLine.cmd_help): Mention 'define' subcommand.
  (RecurrenceCommandLine.cmd_quit): If there are local mods, prompt to save.
  (RecurrenceCommandLine.cmd_save): Now use prompt() instead of confirm().
cmpilato/recurrence