Implemented client side send operation

Implemented send operation for client side, send operation was
introduced with the LwM2M 1.1 standard.
This PR is based on work from @sbertin-telular, specifically on
send branch: https://github.com/sbertin-telular/wakaama/tree/send
In this PR a bug that caused a memory leak has been fixed:
sbertin-telular#1

core/internals.h

@@ -157,6 +157,8 @@
 #define URI_REGISTRATION_SEGMENT_LEN    2
 #define URI_BOOTSTRAP_SEGMENT           "bs"
 #define URI_BOOTSTRAP_SEGMENT_LEN       2
+#define URI_SEND_SEGMENT                "dp"
+#define URI_SEND_SEGMENT_LEN            2
 
 #define QUERY_STARTER        "?"
 #define QUERY_NAME           "ep="
@@ -320,6 +322,9 @@ int object_getRegisterPayload(lwm2m_context_t * contextP, uint8_t * buffer, size
 int object_getServers(lwm2m_context_t * contextP, bool checkOnly);
 uint8_t object_createInstance(lwm2m_context_t * contextP, lwm2m_uri_t * uriP, lwm2m_data_t * dataP);
 uint8_t object_writeInstance(lwm2m_context_t * contextP, lwm2m_uri_t * uriP, lwm2m_data_t * dataP);
+#ifndef LWM2M_VERSION_1_0
+uint8_t object_readCompositeData(lwm2m_context_t * contextP, lwm2m_uri_t * uriP, size_t numUris, int * sizeP, lwm2m_data_t ** dataP);
+#endif
 
 // defined in transaction.c
 lwm2m_transaction_t * transaction_new(void * sessionH, coap_method_t method, char * altPath, lwm2m_uri_t * uriP, uint16_t mID, uint8_t token_len, uint8_t* token);
@@ -458,4 +463,4 @@ lwm2m_server_t * utils_findBootstrapServer(lwm2m_context_t * contextP, void * fr
 lwm2m_client_t * utils_findClient(lwm2m_context_t * contextP, void * fromSessionH);
 #endif
 
-#endif
+#endif