Add option to parse only final entries in task stores.

Refs #9.
Display old task time with switch subcommand.

This is to match the behaviour from a manual stop & start.  Closes #10.
Only parse partial data where possible in command line.

Closes #9.
Fix invalid dirty generation in test_write_database().

The iteration over events caused duplicates.
Append to existing task stores to limit writes.

Closes #11.
Merge branch 'feat/shallow_parse'

* feat/shallow_parse:
  Only parse partial data where possible in command line.
  Add option to parse only final entries in task stores.
Merge branch 'feat/shallow_write'

* feat/shallow_write:
  Append to existing task stores to limit writes.