Transition sample code projects overviews to _index.jd.

Support doc-defined hdf metadata as well as make or doclava-defined hdf metadata. Make breadcrumb dirs optionally linkable and generate index files.

Change-Id: I0b45868033a1136c87bfae7ecdf5a150c85906a5
diff --git a/src/com/google/doclava/Errors.java b/src/com/google/doclava/Errors.java
index e890aa4..c0ba831 100644
--- a/src/com/google/doclava/Errors.java
+++ b/src/com/google/doclava/Errors.java
@@ -170,6 +170,7 @@
   public static final Error NO_FEDERATION_DATA = new Error(117, WARNING);
   public static final Error BROKEN_SINCE_FILE = new Error(118, ERROR);
   public static final Error INVALID_CONTENT_TYPE = new Error(119, ERROR);
+  public static final Error INVALID_SAMPLE_INDEX = new Error(120, ERROR);
 
   public static final Error[] ERRORS =
       {UNRESOLVED_LINK, BAD_INCLUDE_TAG, UNKNOWN_TAG, UNKNOWN_PARAM_TAG_NAME,