Fix freertos.org link in the source and doxygen files (#177)

Author: chinglee-iot

docs/doxygen/pages.dox

@@ -366,14 +366,14 @@ bool PlatformMutex_TryLock( PlatformMutex_t * pMutex );
 void PlatformMutex_Unlock( PlatformMutex_t * pMutex );
 ```
  - <b>Memory</b><br>The following malloc/free style APIs should be provided in cellular_platform.h.<br>
- The <a href="https://www.freertos.org/a00111.html">FreeRTOS memory management document</a> can be referenced for these APIs.
+ The <a href="https://freertos.org/Documentation/02-Kernel/02-Kernel-features/09-Memory-management/01-Memory-management">FreeRTOS memory management document</a> can be referenced for these APIs.
 ```
 // Example implementation of FreeRTOS malloc/free
 #define Platform_Malloc    pvPortMalloc
 #define Platform_Free      vPortFree
 ```
  - <b>EventGroup</b><br>The following APIs and handle should be provided in cellular_platform.h.<br>
- Please reference <a href="https://www.freertos.org/event-groups-API.html">FreeRTOS EvengGroup function prototypes</a>.
+ Please reference <a href="https://freertos.org/Documentation/02-Kernel/04-API-references/12-Event-groups-or-flags/00-Event-groups">FreeRTOS EvengGroup function prototypes</a>.
 ```
 // Example implementation of FreeRTOS EvengGroup
 #define PlatformEventGroupHandle_t           EventGroupHandle_t
@@ -387,7 +387,7 @@ void PlatformMutex_Unlock( PlatformMutex_t * pMutex );
 #define PlatformEventGroup_WaitBits          xEventGroupWaitBits
 ```
  - <b>Queue</b><br>The following APIs and handle should be provided in cellular_platform.h.<br>
- Please reference <a href="https://freertos.org/a00018.html">FreeRTOS Queue function prototypes</a>.
+ Please reference <a href="https://freertos.org/Documentation/02-Kernel/04-API-references/06-Queues/00-QueueManagement">FreeRTOS Queue function prototypes</a>.
 ```
 // Example implementation of FreeRTOS Queue
 #define PlatformQueueHandle_t    QueueHandle_t
@@ -397,7 +397,7 @@ void PlatformMutex_Unlock( PlatformMutex_t * pMutex );
 #define PlatformQueue_Delete     vQueueDelete
 ```
  - <b>Delay</b><br>The following API should be provided in cellular_platform.h.<br>
- Please reference <a href="https://www.freertos.org/a00127.html">FreeRTOS Task Control function prototypes</a>.
+ Please reference <a href="https://freertos.org/Documentation/02-Kernel/04-API-references/02-Task-control/00-Task-control">FreeRTOS Task Control function prototypes</a>.
 ```
 // Example implementation of FreeRTOS Task Control
 #define Platform_Delay( delayMs )           vTaskDelay( pdMS_TO_TICKS( delayMs ) )

test/cbmc/include/cellular_platform.h

@@ -41,7 +41,7 @@
  * Cellular library use platform event group for process synchronization.
  *
  * The EventGroup functions in the following link can be referenced as function prototype.
- * https://www.freertos.org/event-groups-API.html
+ * https://freertos.org/Documentation/02-Kernel/04-API-references/12-Event-groups-or-flags/00-Event-groups
  *
  */
 
@@ -236,7 +236,7 @@ uint16_t PlatformEventGroup_GetBits( PlatformEventGroupHandle_t groupEvent );
  *
  * Cellular library use platform memory allocation APIs to allocate memory dynamically.
  * The FreeRTOS memory management document can be referenced for these APIs.
- * https://www.freertos.org/a00111.html
+ * https://freertos.org/Documentation/02-Kernel/02-Kernel-features/09-Memory-management/01-Memory-management
  *
  */
 

test/unit-test/cellular_platform.h

@@ -78,7 +78,7 @@
  *
  * Cellular library use platform memory allocation APIs to allocate memory dynamically.
  * The FreeRTOS memory management document can be referenced for these APIs.
- * https://www.freertos.org/a00111.html
+ * https://freertos.org/Documentation/02-Kernel/02-Kernel-features/09-Memory-management/01-Memory-management
  *
  */
 
@@ -205,7 +205,7 @@ bool Platform_CreateDetachedThread( void ( * threadRoutine )( void * pArgument )
  * Cellular library use platform event group for process synchronization.
  *
  * The EventGroup functions in the following link can be referenced as function prototype.
- * https://www.freertos.org/event-groups-API.html
+ * https://freertos.org/Documentation/02-Kernel/04-API-references/12-Event-groups-or-flags/00-Event-groups
  *
  */
 bool PlatformMutex_Create( PlatformMutex_t * pNewMutex,