Add additional anchor to match GitHub TOC rendering

GitHub uses lowercase for anchor links, and correspondingly any TOC
references are written to use the same. This results in TOC's that work
when viewed in GitHub, but are broken in Gitiles, and vice-versa.

Add a second anchor using lowercase for the name and id to ensure that it
matches the GitHub flavour of markdown, without breaking existing usage.

Change-Id: I7a07430b183315e0d1433c4ff227a46e5c51bff3

gitiles-servlet/src/main/java/com/google/gitiles/doc/MarkdownToHtml.java

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/doc/MarkdownToHtml.java b/gitiles-servlet/src/main/java/com/google/gitiles/doc/MarkdownToHtml.java
index 99f1c53..d4297dc 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/doc/MarkdownToHtml.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/doc/MarkdownToHtml.java
@@ -215,6 +215,14 @@
           .open("span")
           .close("span")
           .close("a");
+      // github markdown compatibility
+      html.open("a")
+          .attribute("class", "h")
+          .attribute("name", id.toLowerCase())
+          .attribute("href", "#" + id.toLowerCase())
+          .open("span")
+          .close("span")
+          .close("a");
     }
     visitChildren(node);
     html.close(tag);