Docs redesign (#728)

* Adding a dark mode
* Adding reference for types to summary pages
* Adding API Reference
* Adding modifiers to methods/fields/etc
* Minimizing files input
* Caching a lot of the output pages
* Cache only for each execution
* Adding API references to existing docs

docs/input/api/Sections/_Syntax.cshtml

@@ -0,0 +1,8 @@
+@using Statiq.CodeAnalysis
+@{
+    string syntax = Document.GetString(CodeAnalysisKeys.Syntax);
+    if (!syntax.IsNullOrWhiteSpace())
+    {
+        <pre class="language-csharp"><code class="language-csharp">@syntax</code></pre>
+    }
+}