(CHISE_Attribute_Table): Use <DB> instead of <struct

(CHISE_Attribute_Table): Use <DB> instead of <struct
CHISE_Attribute_Table>.
(chise_put_attribute_table): New prototype.
(struct CHISE_Decoding_Table): Use <CHISE_Attribute_Table *> instead
of <DB *> as the type of member `db'.
(chise_ds_open_decoding_table): New implementation.
(chise_dt_close): Likewise.
(chise_dt_get_char): Modify for new implementation of <struct
CHISE_Decoding_Table>.
(chise_dt_put_char): Likewise.
(struct CHISE_Feature_Table): Use <CHISE_Attribute_Table *> instead
of <DB *> as the type of member `db'.
(chise_ds_open_feature_table): New implementation.
(chise_ft_close): Likewise.
(chise_ft_get_value): Modify for new implementation of <struct
CHISE_Feature_Table>.
(chise_open_attribute_table): Use db_dir instead of ds as the first
argument; modify for new implementation of <CHISE_Attribute_Table>.
(chise_close_attribute_table): Modify for new implementation of
<CHISE_Attribute_Table>.
(chise_get_attribute_table): Likewise.
(chise_put_attribute_table): Likewise.