MQTT C Client Libraries Internals: Globals

| MQTT C Client Libraries Internals

- MQTTPersistence_afterRead : MQTTClientPersistence.h
- MQTTPersistence_beforeWrite : MQTTClientPersistence.h
- Persistence_clear : MQTTClientPersistence.h
- Persistence_close : MQTTClientPersistence.h
- Persistence_containskey : MQTTClientPersistence.h
- Persistence_get : MQTTClientPersistence.h
- Persistence_keys : MQTTClientPersistence.h
- Persistence_open : MQTTClientPersistence.h
- Persistence_put : MQTTClientPersistence.h
- Persistence_remove : MQTTClientPersistence.h