add some Default() implementations

https://rust-lang.github.io/rust-clippy/master/index.html#new_without_default

src/lib/book.rs

@@ -1716,6 +1716,12 @@ impl Book {
     }
 }
 
+impl std::default::Default for Book {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 /// Calls mustache::compile_str but catches panics and returns a result
 pub fn compile_str<O>(template: &str, source: O, template_name: &str) -> Result<mustache::Template>
 where

src/lib/book_bars.rs

@@ -56,6 +56,12 @@ impl Bars {
     }
 }
 
+impl Default for Bars {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 /// Return the style of a bar
 
 impl Book {

src/lib/bookoptions.rs

@@ -1088,3 +1088,9 @@ impl BookOptions {
         out
     }
 }
+
+impl Default for BookOptions {
+    fn default() -> Self {
+        Self::new()
+    }
+}

src/lib/parser.rs

@@ -67,6 +67,12 @@ impl Features {
     }
 }
 
+impl Default for Features {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl BitOr for Features {
     type Output = Self;
 
@@ -395,6 +401,12 @@ impl Parser {
     }
 }
 
+impl Default for Parser {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 /// Replace consecutives Strs by a Str of both, collapse soft breaks to previous std and so on
 fn collapse(ast: &mut Vec<Token>) {
     let mut i = 0;

src/lib/resource_handler.rs

@@ -236,6 +236,12 @@ impl ResourceHandler {
     }
 }
 
+impl Default for ResourceHandler {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 /// Get the list of all files, walking recursively in directories
 ///
 /// # Arguments