Refactor with the help of Clippy (#462)

We add clippy as our build — also rectifying the missing `plume-cli` build!

In the next step we follow clippy's advise and fix some of the "simple" mistakes in our code, such as style or map usage.

Finally, we refactor some hard bits that need extraction of new types, or refactoring of function call-types, especially those that thread thru macros, and, of course functions with ~15 parameters should probably be rethought.

templates/posts/details.rs.html

@@ -23,8 +23,8 @@
     <a href="@uri!(blogs::details: name = &blog.fqn, page = _)">@blog.title</a>
 }, {
 <div class="h-entry">
-    <h1 class="article p-name">@&article.title</h1>
-    <h2 class="article p-summary">@&article.subtitle</h2>
+    <h1 class="article p-name">@article.title</h1>
+    <h2 class="article p-summary">@article.subtitle</h2>
     <div class="article-info">
         <span class="author">
             @Html(i18n!(ctx.1, "Written by {0}"; format!("<a href=\"{}\">{}</a>",

templates/posts/new.rs.html

@@ -27,7 +27,7 @@
         @input!(ctx.1, subtitle (optional text), "Subtitle", form, errors.clone(), "")
 
         @if let Some(ValidationErrorsKind::Field(errs)) = errors.clone().errors().get("content") {
-            @format!(r#"<p class="error">{}</p>"#, errs[0].message.clone().unwrap_or(Cow::from("Unknown error")))
+            @format!(r#"<p class="error">{}</p>"#, errs[0].message.clone().unwrap_or_else(|| Cow::from("Unknown error")))
         }
 
         <label for="editor-content">@i18n!(ctx.1, "Content")<small>@i18n!(ctx.1, "Markdown syntax is supported")</small></label>