Get Record#id from record.value.key.id
Add test_size, test_empty?, test_each
Add test_read_by_key, test_write_by_key
Add test_delete_by_id, test_delete_by_block
Change TestGrnMiniHash::test_each
Add test_float_column, test_time_column, test_record_attributes, test_assign_long_text_to_short_text
Add test_grn_object
Add test_sort, test_group_from_hash