Defaults to 04:00 instead of 00:00 when no time is provided for the document creation time. 04:00 is the first time that is both morning and not night.
Adds support for combining time spans with unspecified periods to get PAST_REF and FUTURE_REF
Improves sample grammar and adds more annotation errors and expected failures
Adds support for DECADE_OF_CENTURY
Adds several rules to sample grammar
Filters out semantically impossible parses in TimeNormalizer.normalize