- Removed support for ' 1 wk', namely spaces before and after the ordinal.
This removes (some) ambiguity in more complex command lines.
- Fixed unit tests accordingly.
- Allowed durations to be specified numerically as seconds, in string form.
This flexibility allows the removal of special-case handling that stores
recurrence periods in raw form ('monthly'), reducing code size. As a
consequence this means that recurrence may now be rendered according to
Duration::formatCompact, which is desirable.
- Added supporting unit tests.