Add an initial implementation of PlainLink.

src/parser/object.rs

@@ -76,7 +76,8 @@ pub struct RadioLink<'s> {
 #[derive(Debug, PartialEq)]
 pub struct PlainLink<'s> {
     pub source: &'s str,
-    pub children: Vec<Object<'s>>,
+    pub link_type: &'s str,
+    pub path: &'s str,
 }
 
 impl<'s> Source<'s> for Object<'s> {