MXS-1220: Add session JSON output

Sessions can now be printed in JSON.

include/maxscale/session.h

@@ -25,6 +25,7 @@
 #include <maxscale/log_manager.h>
 #include <maxscale/resultset.h>
 #include <maxscale/spinlock.h>
+#include <maxscale/jansson.h>
 
 MXS_BEGIN_DECLS
 
@@ -412,4 +413,13 @@ bool session_take_stmt(MXS_SESSION *session, GWBUF **buffer, const struct server
  */
 void session_clear_stmt(MXS_SESSION *session);
 
+/**
+ * @brief Convert a session to JSON
+ *
+ * @param session Session to convert
+ *
+ * @return New JSON object or NULL on error
+ */
+json_t* session_to_json(const MXS_SESSION *session);
+
 MXS_END_DECLS