add HDF variable for 'referenceonly' based on the -referenceonly command flag.
This is used in the templates to decide which tabs to show.

Change-Id: I53e0f461ca8e03341a737d8f201bab454e06ce8f
diff --git a/src/com/google/doclava/Doclava.java b/src/com/google/doclava/Doclava.java
index 32b9b81..825c8f8 100644
--- a/src/com/google/doclava/Doclava.java
+++ b/src/com/google/doclava/Doclava.java
@@ -285,6 +285,7 @@
         documentAnnotationsPath = a[1];
       } else if (a[0].equals("-referenceonly")) {
         referenceOnly = true;
+        mHDFData.add(new String[] {"referenceonly", "1"});
       }
     }