Phase 1: Refactor DateParser structure

- Create DateParser struct with configurable base time and week start
- Add placeholder methods for new parsing features
- Implement time-of-day parsing foundation (splitDateTime, parseTimeOfDay)
- Maintain backward compatibility with existing ParseDate() function
- Update tests to use new DateParser API
- All 33 existing tests passing

opal-task/TIME.md

@@ -0,0 +1,28 @@
+# Time parsing
+
+## Time formats
+- mon, monday - sun, sunday
+- 21jan, 30dec etc
+- 2015-12-21
+- jan, feb, etc. - Sets to first of month
+- now, current date and time
+- today, tomorrow, yesterday - at time 00:00
+- sod, sow, som, soy - start of X at time 00:00
+- eod, eow, eom, eoy - end of X at time 23:59
+- later, someday - 2150-01-01 at time 00:00
+
+All time formats should also support time of day, mon:15:35 and mon:1535. 24-hour format. Mind the ':', must be seperated from the attribute:value syntax.
+
+## Duration formats
+- 5sec, second, seconds
+- 5min, minute, minutes 
+- 5hrs, hour, hours 
+- 3d[ays], 2w[eeks], 4m[onths], 1y[ear]. Singular if 1, plural >1
+- daily, weekly, monthly (30days), yearly
+
+There is indirect support for durations everywhere that a date value is expected.
+No ordinal assumes 1 (hours = hrs = hour = 60min)
+
+## Relative formats
+One attribute can be relative to another:
+`opal add Buy milk due:mon wait:due-1d`