notmuch_database_set_config (notmuch_database_t *db, const char *key, const char *value);
notmuch_status_t
notmuch_database_get_config (notmuch_database_t *db, const char *key, char **value);
notmuch_database_set_config (notmuch_database_t *db, const char *key, const char *value);
notmuch_status_t
notmuch_database_get_config (notmuch_database_t *db, const char *key, char **value);