Add rake rdoc task
Adjust position of require statements
Remove old copyright notice
Improve process communication mhc and emacs
Drop support for X-SC-Priority
Ensure to use Mhc::PropertyValue::Date instead of Date
Introduce X-SC-Sequence

This is preparation for good synchronization
with Google calendar.

Sequence should start from zero and
be incremented each time event is updated.
This is necessary for synchronization with iCalendar
based systems.
DateEnumerator::ByRangeList not to flatten the range on enumeration
Sync with google calendar

Although, it is actually one way from mhc to GC,
it has pretty good conversion from existing articles
into iCalendar including recurrences.