v0.22.0

F311-01: CREATE SCHEMA (#111)

This adds support for `F311-01`: `CREATE SCHEMA` from `F311`:
"Schema definition statement" and the respective `DROP SCHEMA` (even
through that's not strictly required for `F311`). For example:

    CREATE SCHEMA warehouse;

    CREATE TABLE warehouse.products (
        title CHARACTER VARYING(100),
        price FLOAT
    );

    DROP SCHEMA warehouse CASCADE;