Add formatted body

src/client.rs

 pub struct OutgoingGist {
     pub title: String,
     pub body: String,
+    pub formatted_body: String,
     pub filetype: Option<String>,
 }
 
     let gist = OutgoingGist {
         title: title.to_string(),
         body: body.to_string(),
+        formatted_body: String::from(""),
         filetype: filetype.map(|ft| ft.to_string()),
     };