Simplify the use of `Option::and_then`

I found a few places where `Option::and_then` could be simplified (in
my opinion) with `?` or with `match`.

src/cmd/serve.rs

@@ -89,8 +89,7 @@ pub fn execute(args: &ArgMatches) -> Result<()> {
     let input_404 = book
         .config
         .get("output.html.input-404")
-        .map(toml::Value::as_str)
+        .and_then(toml::Value::as_str)
-        .and_then(std::convert::identity) // flatten
         .map(ToString::to_string);
     let file_404 = get_404_output_file(&input_404);
 

src/renderer/html_handlebars/helpers/navigation.rs

@@ -148,15 +148,12 @@ fn render(
 
     trace!("Render template");
 
-    _h.template()
+    let t = _h
-        .ok_or_else(|| RenderError::new("Error with the handlebars template"))
+        .template()
-        .and_then(|t| {
+        .ok_or_else(|| RenderError::new("Error with the handlebars template"))?;
     let local_ctx = Context::wraps(&context)?;
     let mut local_rc = rc.clone();
     t.render(r, &local_ctx, &mut local_rc, out)
-        })?;
-
-    Ok(())
 }
 
 pub fn previous(

src/renderer/html_handlebars/helpers/toc.rs

@@ -117,13 +117,11 @@ impl HelperDef for RenderToc {
             }
 
             // Link
-            let path_exists = if let Some(path) =
+            let path_exists: bool;
-                item.get("path")
+            match item.get("path") {
-                    .and_then(|p| if p.is_empty() { None } else { Some(p) })
+                Some(path) if !path.is_empty() => {
-            {
                     out.write("<a href=\"")?;
-
+                    let tmp = Path::new(path)
-                let tmp = Path::new(item.get("path").expect("Error: path should be Some(_)"))
                         .with_extension("html")
                         .to_str()
                         .unwrap()
@@ -141,11 +139,13 @@ impl HelperDef for RenderToc {
                     }
 
                     out.write(">")?;
-                true
+                    path_exists = true;
-            } else {
+                }
+                _ => {
                     out.write("<div>")?;
-                false
+                    path_exists = false;
-            };
+                }
+            }
 
             if !self.no_section_label {
                 // Section does not necessarily exist