Annotate the public/confidential/shared parts of the BE template.

Rewrite some examples that used internal labels to be safe for external
version.  Also remove some obsolete parts such as no-longer existent Make
variables.

--
MOS_MIGRATED_REVID=87241538
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 a2e7583..161d7b6 100644
--- a/src/main/java/com/google/devtools/build/docgen/DocgenConsts.java
+++ b/src/main/java/com/google/devtools/build/docgen/DocgenConsts.java
@@ -13,6 +13,8 @@
 // limitations under the License.
 package com.google.devtools.build.docgen;
 
+import com.google.common.base.Joiner;
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.devtools.build.lib.util.FileType;
 import com.google.devtools.build.lib.util.FileTypeSet;
@@ -62,13 +64,16 @@
   public static final String FLAG_DEPRECATED = "DEPRECATED";
   public static final String FLAG_GENERIC_RULE = "GENERIC_RULE";
 
-  public static final String HEADER_COMMENT =
-      "<!DOCTYPE html>\n"
-      + "<!--\n"
-      + " This document is synchronized with Blaze releases.\n"
-      + " To edit, submit changes to the Blaze source code.\n"
-      + " Generated by: blaze build java/com/google/devtools/build/docgen:build-encyclopedia.html\n"
-      + "-->\n";
+  public static final String HEADER_COMMENT = Joiner.on("\n").join(ImmutableList.<String>of(
+      "<!-- begin-block:shared -->",
+      "<!DOCTYPE html>",
+      "<!--",
+      " This document is synchronized with Blaze releases.",
+      " To edit, submit changes to the Blaze source code.",
+      "-->",
+      "",
+      "<!-- begin-block:internal -->",
+      "<!-- Generated by //java/com/google/devtools/build/docgen:build-encyclopedia.html -->"));
 
   public static final String BUILD_ENCYCLOPEDIA_NAME = "build-encyclopedia.html";