docket 0.15.0

Added

• gg and G jump the graph viewer to the first and last record. g is a
  prefix key, and any other key clears it and then runs normally.
• s cycles the graph viewer's sort field through ledger order, id, timestamp,
  kind and state, and r reverses the direction. A sort reorders roots only and
  each subtree moves with its root, so a support tree stays readable. The
  selection follows the record across a re-sort, and the footer names the active
  field and direction.