Add templates for text markup.

src/context/plain_text.rs

@@ -9,15 +9,19 @@ use crate::intermediate::IPlainText;
 #[derive(Debug, Serialize)]
 #[serde(tag = "type")]
 #[serde(rename = "plain_text")]
-pub(crate) struct RenderPlainText {}
+pub(crate) struct RenderPlainText {
+    source: String,
+}
 
 impl RenderPlainText {
     pub(crate) fn new(
         config: &Config,
         output_directory: &Path,
         output_file: &Path,
-        heading: &IPlainText,
+        original: &IPlainText,
     ) -> Result<RenderPlainText, CustomError> {
-        Ok(RenderPlainText {})
+        Ok(RenderPlainText {
+            source: original.source.clone(),
+        })
     }
 }

src/intermediate/plain_text.rs

@@ -5,7 +5,7 @@ use super::registry::Registry;
 
 #[derive(Debug)]
 pub(crate) struct IPlainText {
-    source: String,
+    pub(crate) source: String,
 }
 
 impl IPlainText {