usermanual: update list of contributors
dt_tag_detach_by_string(): use DT_DEBUG_SQLITE3_PREPARE_V2
dt_tag_get_suggestions(): use DT_DEBUG_SQLITE3_PREPARE_V2
dt_tag_reorganize(): use DT_DEBUG_SQLITE3_PREPARE_V2

FIXME: dt_tag_reorganize() appears to be unused?