Clean up serialize interface.

Switch to jansson for JSON handling.
Add server ID.
Expose IDs in JSON.

client.h

@@ -2,8 +2,6 @@
 
 #include "common.h"
 
-#define SERIALIZE_LEN 256
-
 
 struct serializer *client_get_serializer(char *);
 void client_add(int, struct serializer *);