Reduce technical depts

This includes:
    - Use 'Self' instead of '<type name>' where possible.
    - Match enums in order of their variants.

src/book/book.rs

@@ -136,13 +136,13 @@ pub enum BookItem {
 }
 
 impl From<Chapter> for BookItem {
-    fn from(other: Chapter) -> BookItem {
+    fn from(other: Chapter) -> Self {
         BookItem::Chapter(other)
     }
 }
 
 impl From<VirtualChapter> for BookItem {
-    fn from(other: VirtualChapter) -> BookItem {
+    fn from(other: VirtualChapter) -> Self {
         BookItem::VirtualChapter(other)
     }
 }
@@ -199,8 +199,8 @@ pub struct VirtualChapter {
 
 impl VirtualChapter {
     /// Create a new chapter with the provided content.
-    pub fn new(name: &str, content: String) -> VirtualChapter {
-        VirtualChapter {
+    pub fn new(name: &str, content: String) -> Self {
+        Self {
             name: name.to_string(),
             content: content,
             ..Default::default()
@@ -246,6 +246,7 @@ fn load_summary_item<P: AsRef<Path>>(
             load_chapter(link, src_dir, parent_names).map(|c| BookItem::Chapter(c))
         }
         SummaryItem::VirtualLink(ref link) => unimplemented!(),
+        SummaryItem::Separator => Ok(BookItem::Separator),
     }
 }
 

src/book/summary.rs

@@ -79,8 +79,8 @@ pub struct Link {
 
 impl Link {
     /// Create a new link with no nested items.
-    pub fn new<S: Into<String>, P: AsRef<Path>>(name: S, location: P) -> Link {
-        Link {
+    pub fn new<S: Into<String>, P: AsRef<Path>>(name: S, location: P) -> Self {
+        Self {
             name: name.into(),
             location: location.as_ref().to_path_buf(),
             number: None,
@@ -91,7 +91,7 @@ impl Link {
 
 impl Default for Link {
     fn default() -> Self {
-        Link {
+        Self {
             name: String::new(),
             location: PathBuf::new(),
             number: None,
@@ -115,8 +115,8 @@ pub struct VirtualLink {
 
 impl VirtualLink {
     /// Create a new virtual link with no nested items.
-    pub fn new<S: Into<String>>(name: S) -> VirtualLink {
-        VirtualLink {
+    pub fn new<S: Into<String>>(name: S) -> Self {
+        Self {
             name: name.into(),
             number: None,
             nested_items: Vec::new(),
@@ -126,7 +126,7 @@ impl VirtualLink {
 
 impl Default for VirtualLink {
     fn default() -> Self {
-        VirtualLink {
+        Self {
             name: String::new(),
             number: None,
             nested_items: Vec::new(),
@@ -163,13 +163,13 @@ impl SummaryItem {
 }
 
 impl From<Link> for SummaryItem {
-    fn from(other: Link) -> SummaryItem {
+    fn from(other: Link) -> Self {
         SummaryItem::Link(other)
     }
 }
 
 impl From<VirtualLink> for SummaryItem {
-    fn from(other: VirtualLink) -> SummaryItem {
+    fn from(other: VirtualLink) -> Self {
         SummaryItem::VirtualLink(other)
     }
 }