Add title to heading object.

src/parser/document.rs

@@ -43,6 +43,7 @@ pub struct Document<'s> {
 pub struct Heading<'s> {
     pub source: &'s str,
     pub stars: usize,
+    pub title: Vec<Object<'s>>,
     pub children: Vec<DocumentElement<'s>>,
 }
 
@@ -131,6 +132,7 @@ fn heading<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, Hea
         Heading {
             source,
             stars: star_count,
+            title,
             children,
         },
     ))