Allow to create javadocs for multiple packages

Change-Id: Ia3de0458603dbe14f510b2edadf6ea44406b820e
diff --git a/java_doc.bucklet b/java_doc.bucklet
index 1a0a240..57e3367 100644
--- a/java_doc.bucklet
+++ b/java_doc.bucklet
@@ -19,7 +19,7 @@
 # java_doc(
 #   name = 'javadoc',
 #   title = 'Gitiles API Documentation',
-#   pkg = 'com.google.gitiles',
+#   pkgs = ['com.google.gitiles'],
 #   paths = ['gitiles-servlet/src/main/java'],
 #   srcs = glob([n + '**/*.java' for n in SRCS]),
 #   deps = DEPS,
@@ -29,7 +29,7 @@
 def java_doc(
     name,
     title,
-    pkg,
+    pkgs,
     paths,
     srcs = [],
     deps = [],
@@ -52,7 +52,8 @@
       '-notimestamp',
       '-windowtitle "' + title + '"',
       '-link http://docs.oracle.com/javase/7/docs/api',
-      '-subpackages ' + pkg,
+      '-subpackages ',
+      ':'.join(pkgs),
       '-sourcepath ',
       ':'.join(sourcepath),
       ' -classpath ',