Implement the new fields for paragraph.

src/types/lesser_element.rs

@@ -25,6 +25,8 @@ use crate::error::Res;
 #[derive(Debug)]
 pub struct Paragraph<'s> {
     pub source: &'s str,
+    pub contents: Option<&'s str>,
+    pub post_blank: Option<&'s str>,
     pub affiliated_keywords: AffiliatedKeywords<'s>,
     pub children: Vec<Object<'s>>,
 }
@@ -189,6 +191,8 @@ impl<'s> Paragraph<'s> {
     pub(crate) fn of_text(source: &'s str, body: &'s str) -> Self {
         Paragraph {
             source,
+            contents: None,   // TODO
+            post_blank: None, // TODO
             affiliated_keywords: AffiliatedKeywords::default(),
             children: vec![Object::PlainText(PlainText { source: body })],
         }
@@ -201,11 +205,15 @@ impl<'s> StandardProperties<'s> for Paragraph<'s> {
     }
 
     fn get_contents<'b>(&'b self) -> Option<&'s str> {
-        todo!()
+        self.contents
     }
 
     fn get_post_blank(&self) -> PostBlank {
-        todo!()
+        self.post_blank
+            .map(|text| text.lines().count())
+            .unwrap_or(0)
+            .try_into()
+            .expect("Too much post-blank to fit into a PostBlank.")
     }
 }