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/_Attributes.cshtml

@@ -0,0 +1,26 @@
+@using Statiq.CodeAnalysis
+@using Docs.Extensions
+@{
+    IReadOnlyList<IDocument> attributes = Document.GetDocumentList(CodeAnalysisKeys.Attributes);
+    if (attributes?.Count > 0)
+    {
+        <h3>Attributes</h3>
+        <div class="doc-summary">
+            <div>
+                <dl>
+                    @foreach (var attribute in attributes)
+                    {
+                        var type = attribute.GetDocument(CodeAnalysisKeys.Type);
+
+                        <div>
+                            <dt>
+                                @Context.GetTypeLink(type)
+                            </dt>
+                            <dd>@Html.Raw(type.GetString(CodeAnalysisKeys.Summary))</dd>
+                        </div>
+                    }
+                </dl>
+            </div>
+        </div>
+    }
+}