Convert the rest of the date calculations to use the date_ymd struct
Add handling of monthfirst/dayfirst ambiguous dates
Optimize the month and weekday string matching a little bit
Implement the time type

Biggest missing feature, aside from time zones, is
parsing from strings
Move common functionality from date_parser.cpp into parser_util.hpp/cpp
Add saved_begin_state for parser, get simple time parsing working
Get the time parser into basic working shape
Adjustments from PR review
Merge pull request #23 from mwiebe/time_type

Implement time type