Add anchor-based TOC navigation: parse #fragment anchors, find exact page within section

src/app.rs

@@ -382,6 +382,15 @@ BgType::Custom(ref path) if !path.is_empty() => {
             if let Some(section) = action.jump_to_section {
                 self.state.current_section = section;
                 self.state.current_page = 0;
+                if let Some(ref anchor) = action.jump_to_anchor {
+                    if let Some(ref book) = self.state.book {
+                        if section < book.sections.len() {
+                            if let Some(page) = crate::reader::find_page_for_anchor(&book.sections[section], anchor) {
+                                self.state.current_page = page;
+                            }
+                        }
+                    }
+                }
             }
 
             if action.page_prev {