State.save

int save(LV2_URID_Map *  map,  LV2_URID_Unmap *  unmap,  string uri,  string dir,
            string filename)

Save this state to a bundle directory / file on disk.

`map`	URID map
`unmap`	URID unmap
`uri`	Absolute state URI, or null to use a file URI based on dir/filename
`dir`	Directory to save into (created if needed)
`filename`	State file name within dir (e.g. "state.ttl"), or null

0 on success