Performance

- Removed Context::timer_sync, as it makes no sense now that sync is not an
  automatic operation like gc.
Merge branch '2.3.0' of tasktools.org:task into 2.3.0
Bug #1211

- #1211 The 'dateformat' settings now default to the ISO-8601 standard of
  'Y-M-D' (thanks to Robin Björklin).