Implement conversions for Line, GeometryCollection, Rect, Triangle

[urschrei]

Currently, this causes a run-time panic!(), which is not great. Line, Triangle and Rect should be easy to implement, but what about GeometryCollection?

[urschrei]

Line maps to GeoJSON LineString
Triangle and Rect map to GeoJSON Polygon
GeometryCollection maps to GeoJSON GeometryCollection

[frewsxcv]

Relevant code that needs to change:

geojson/src/conversion/from_geo_types.rs

Lines 101 to 121 in f394a5b

	#[cfg_attr(docsrs, doc(cfg(feature = "geo-types")))]
	impl<'a, T> From<&'a geo_types::Geometry<T>> for geometry::Value
	where
	T: Float,
	{
	fn from(geometry: &'a geo_types::Geometry<T>) -> Self {
	match *geometry {
	geo_types::Geometry::Point(ref point) => geometry::Value::from(point),
	geo_types::Geometry::MultiPoint(ref multi_point) => geometry::Value::from(multi_point),
	geo_types::Geometry::LineString(ref line_string) => geometry::Value::from(line_string),
	geo_types::Geometry::MultiLineString(ref multi_line_string) => {
	geometry::Value::from(multi_line_string)
	}
	geo_types::Geometry::Polygon(ref polygon) => geometry::Value::from(polygon),
	geo_types::Geometry::MultiPolygon(ref multi_polygon) => {
	geometry::Value::from(multi_polygon)
	}
	_ => panic!("GeometryCollection not allowed"),
	}
	}
	}

We should stop using _ as a matching pattern here and make it exhaustive.