Pass `path_html` to HTML renderer

When linking between translations, we can use `path_html` instead of
changing .md to .html with `path`.

src/renderer/html_handlebars/hbs_renderer.rs

@@ -94,6 +94,7 @@ impl HtmlHandlebars {
         };
 
         ctx.data.insert("path".to_owned(), json!(path));
+        ctx.data.insert("path_html".to_owned(), json!(filepath));
         ctx.data.insert("content".to_owned(), json!(content));
         ctx.data.insert("chapter_title".to_owned(), json!(ch.name));
         ctx.data.insert("title".to_owned(), json!(title));