create IntoContent trait and add Comment ContentBuilder type

src/element.rs

@@ -3,7 +3,7 @@
 #![feature(drain_filter)]
 
 use std::{
-    collections::{HashMap, HashSet, VecDeque},
+    collections::{vec_deque, HashMap, HashSet, VecDeque},
     convert::Infallible,
     str::FromStr,
 };
@@ -580,6 +580,10 @@ impl ElementBuilder {
 }
 
 pub trait IntoContent {
+    fn into_content(&self) -> Content {
+        self.builder().build().unwrap()
+    }
+
     fn builder(&self) -> ContentBuilder;
 }
 
@@ -592,9 +596,14 @@ where
     }
 }
 
+pub trait FromContent: Sized {
+    fn from_content(content: Content) -> DeserializeResult<Self>;
+}
+
 pub enum ContentBuilder {
     Element(ElementBuilder),
     Text(String),
+    Comment(String),
 }
 
 impl ContentBuilder {
@@ -604,6 +613,7 @@ impl ContentBuilder {
                 Ok(Content::Element(element_builder.build()?))
             }
             ContentBuilder::Text(text) => Ok(Content::Text(text.to_string())),
+            ContentBuilder::Comment(s) => Ok(Content::Comment(s.to_string())),
         }
     }
 }