Add a logo to the HTML template

The logo is placed at the top of the navication sidebar.

src/renderer/html_handlebars/hbs_renderer.rs

@@ -603,6 +603,10 @@ fn make_data(
         "description".to_owned(),
         json!(config.book.description.clone().unwrap_or_default()),
     );
+    data.insert(
+        "book_logo".to_owned(),
+        json!(config.book.logo.clone().unwrap_or_default()),
+    );
     if theme.favicon_png.is_some() {
         data.insert("favicon_png".to_owned(), json!("favicon.png"));
     }

src/theme/css/chrome.css

@@ -344,6 +344,13 @@ ul#searchresults span.teaser em {
     right: 0;
     padding: 10px 10px;
 }
+.sidebar .sidebar-scrollbox .sidebar-book-logo img {
+    display: block;
+    margin-left: auto;
+    margin-right: auto;
+    width: 100%;
+    max-width: max-content;
+}
 .sidebar .sidebar-resize-handle {
     position: absolute;
     cursor: col-resize;

src/theme/index.hbs

@@ -103,6 +103,11 @@
 
         <nav id="sidebar" class="sidebar" aria-label="Table of contents">
             <div class="sidebar-scrollbox">
+                {{#if book_logo }}
+                <div class="sidebar-book-logo">
+                    <img src="{{ book_logo }}">
+                </div>
+                {{/if}}
                 {{#toc}}{{/toc}}
             </div>
             <div id="sidebar-resize-handle" class="sidebar-resize-handle"></div>