Split Skylark Library into multiple pages, one per module. Add collapsible
submenus to sidebar, and expand and highlight the link for the current page.
Collapse sidebar on mobile and expose button for toggling sidebar.

--
MOS_MIGRATED_REVID=100836792
diff --git a/src/main/java/com/google/devtools/build/docgen/DocgenConsts.java b/src/main/java/com/google/devtools/build/docgen/DocgenConsts.java
index 31f3359..e500588 100644
--- a/src/main/java/com/google/devtools/build/docgen/DocgenConsts.java
+++ b/src/main/java/com/google/devtools/build/docgen/DocgenConsts.java
@@ -32,7 +32,11 @@
   public static final String HEADER_TEMPLATE = "templates/be-header.html";
   public static final String FOOTER_TEMPLATE = "templates/be-footer.html";
   public static final String BODY_TEMPLATE = "templates/be-body.html";
-  public static final String SKYLARK_BODY_TEMPLATE = "templates/skylark-body.html";
+
+  public static final String SKYLARK_LIBRARY_TEMPLATE =
+      "com/google/devtools/build/docgen/templates/skylark-library.vm";
+  public static final String SKYLARK_NAV_TEMPLATE =
+      "com/google/devtools/build/docgen/templates/skylark-nav.vm";
 
   public static final String VAR_LEFT_PANEL = "LEFT_PANEL";