Added some package javadocs and corrected some wording in others.
diff --git a/core/json/src/main/java/org/onlab/onos/json/impl/package-info.java b/core/json/src/main/java/org/onlab/onos/json/impl/package-info.java
new file mode 100644
index 0000000..406641f
--- /dev/null
+++ b/core/json/src/main/java/org/onlab/onos/json/impl/package-info.java
@@ -0,0 +1,4 @@
+/**
+ * Implementation of JSON codec factory and of the builtin codecs.
+ */
+package org.onlab.onos.json.impl;
\ No newline at end of file