Implement SQL:2011 WHERE predicates for application-versioned tables (CONTAINS, OVERLAPS, etc.)

I would like to request the keywords found in section 2.2.3 of "Temporal features in SQL:2011", for DML/DQL of application-versioned tables, be implemented. These include: `CONTAINS`, `OVERLAPS`, `EQUALS`, `PRECEDES`, `SUCCEEDS`, `IMMEDIATELY PRECEDES`, and `IMMEDIATELY SUCCEEDS`.

`CONTAINS` is the most critical, since it is extremely advantageous to be able to query rows that are active now (or at any given point). It is relatively easy to implement in DML (by checking start <= date and end > date), as are all the predicates, but implementing them in the backend would greatly simplify queries.

Sample constructions:

SELECT * from t

WHERE my_period CONTAINS DATE '2011-01-02';

SELECT * from t

WHERE my_period OVERLAPS

    PERIOD (DATE '2010-01-01',

    DATE '2011-01-01');