Tweak test data.

Leave ALIGNED_WEEK_OF_YEAR as is - St. Tib's Day not in week, cannot be
aligned, attempted modification does nothing.
Change DAY_OF_MONTH to have less precedence than MONTH_OF_YEAR
(resolvePreviousValid needs to be modified, but is broken anyways...).
Add adjust tests and method overrides.
Add tests for with(LocalDate)
Add tests for LocalDate.with(DiscordianDate)
Add plus/minus tests and overrides.

Add tests for adding/subtracting periods, and overrides for covariant
return.
Also, adjust with(ALIGNED_WEEK_OF_YEAR) to follow similar behavior as
will be observed with plus/minus.
Add until tests and base implementation (will need to be changed).
Add tests for plus(Period)
Add toString and equals tests.