Log Message:
py-apsw: updated to 3.21.0

3.21.0:
Added constants:

SQLITE_INDEX_CONSTRAINT_ISNULL, SQLITE_INDEX_CONSTRAINT_ISNOT,
SQLITE_INDEX_CONSTRAINT_ISNOTNULL, SQLITE_INDEX_CONSTRAINT_IS and
SQLITE_INDEX_CONSTRAINT_NE

SQLITE_CONFIG_SMALL_MALLOC

SQLITE_IOCAP_BATCH_ATOMIC

SQLITE_IOERR_ROLLBACK_ATOMIC, SQLITE_IOERR_COMMIT_ATOMIC and
SQLITE_IOERR_BEGIN_ATOMIC

SQLITE_FCNTL_COMMIT_ATOMIC_WRITE, SQLITE_FCNTL_ROLLBACK_ATOMIC_WRITE and
SQLITE_FCNTL_BEGIN_ATOMIC_WRITE