wrap multi polygon too

src/geo_types_to_wkt.rs

@@ -1,6 +1,6 @@
 use geo_types::CoordNum;
 
-use crate::to_wkt::write_point;
+use crate::to_wkt::{write_multi_polygon, write_point};
 use crate::types::{
     Coord, GeometryCollection, LineString, MultiLineString, MultiPoint, MultiPolygon, Point,
     Polygon,
@@ -188,6 +188,17 @@ where
     fn to_wkt(&self) -> Wkt<T> {
         g_mpolygon_to_w_mpolygon(self).into()
     }
+
+    fn wkt_string(&self) -> String {
+        let mut s = String::new();
+        write_multi_polygon(&mut s, self).unwrap();
+        s
+    }
+
+    fn write_wkt(&self, writer: impl std::io::Write) -> std::io::Result<()> {
+        write_multi_polygon(&mut WriterWrapper(writer), self).unwrap();
+        Ok(())
+    }
 }
 
 /// # Examples