add separate template for the "latest post" page (the home/main page)

since it's reasonable to assume some may want to customize this a
little differently than the normal post page.

example-site/templates/latest_post.html

@@ -0,0 +1,4 @@
+{% extends "base.html" %}
+{% block content %}
+{% include "partials/post.html" %}
+{% endblock content %}

src/site.rs

@@ -343,7 +343,7 @@ impl SiteService {
 		if let Some(post) = post {
 			context.insert("post", post);
 		}
-		HttpResponse::Ok().body(self.template_renderer.render("post.html", &context).unwrap())
+		HttpResponse::Ok().body(self.template_renderer.render("latest_post.html", &context).unwrap())
 	}
 
 	pub fn serve_posts_by_tag(&self, tag: &Tag) -> HttpResponse {