Added assertSame identity assertion
Added common constants for hours, minutes, seconds and milliseconds
the constants themselves
(re)implement date-time calculations
Merge branch 'constants'

Conflicts:
	.ceylon/config
	.ceylon/config.old
	source/ceylon/time/Date.ceylon
	source/ceylon/time/Period.ceylon
	source/ceylon/time/Time.ceylon
	source/ceylon/time/base/ReadableDate.ceylon
	source/ceylon/time/impl/GregorianDate.ceylon
	source/ceylon/time/impl/GregorianDateTime.ceylon
	source/ceylon/time/impl/TimeOfDay.ceylon
	source/ceylon/time/impl/fields.ceylon
	source/ceylon/time/impl/utils.ceylon
	tests/test/ceylon/time/dates.ceylon
	tests/test/ceylon/time/weekdays.ceylon