RFC: DateTime::Set time_zone()

[Flavio S. Glock]

modules:
  DateTime::Set time_zone()
  DateTime::Span time_zone()
  DateTime::SpanSet time_zone()

time_zone()

  Changes the time_zone of the whole datetime set.

  $set = $set->time_zone( 'America/Los_Angeles' );

Note: it could be named "set_time_zone()", but I think "set" is
ambiguous in this context.

- Flavio S. Glock