doxygen: group name all in lowcase

This patch only updated the groups defined in documentation/0.doxygen.

Other groups will be moved into documentation/0.doxygen and updated at
that time.

Signed-off-by: Chen Wang <unicorn_wang@outlook.com>

documentation/0.doxygen/0.basicdef.h

@@ -3,7 +3,7 @@
  */
 
 /**
- * @defgroup group_BasicDef Basic Definitions
+ * @defgroup group_basic_definition Basic Definitions
  *
  * @brief Basic data type in RT-Thread RTOS.
  *

documentation/0.doxygen/1.core.h

@@ -14,7 +14,7 @@
  */
 
 /**
- * @defgroup group_KernelObject Kernel Object Management
+ * @defgroup group_kernel_object Kernel Object Management
  * @brief See @ref section_kernel_object_model
  *
  * The Kernel object system can access and manage all of the kernel objects.
@@ -34,22 +34,22 @@
  */
 
 /**
- * @defgroup group_Thread Thread Management
+ * @defgroup group_thread_management Thread Management
  * @brief See @ref page_thread_management
  */
 
 /**
- * @defgroup group_Clock Clock and Timer Management
+ * @defgroup group_clock_management Clock and Timer Management
  * @brief See @ref page_clock_management
  */
 
 /**
- * @defgroup group_IPC Inter-Thread Communication
+ * @defgroup group_thread_comm Inter-Thread Communication
  * @brief See @ref page_thread_comm
  */
 
 /**
- * @defgroup group_MM Memory Management
+ * @defgroup group_memory_management Memory Management
  * @brief memory management for memory pool and heap memory
  *
  * RT-Thread operating system supports two types memory management:
@@ -68,7 +68,7 @@
  */
 
 /**
- * @defgroup group_Hook Runtime Trace and Record
+ * @defgroup group_hook Runtime Trace and Record
  * @brief the hook function set in runtime
  *
  * In order to trace and record RT-Thread activity in runtime, a hook mechanism
@@ -83,12 +83,12 @@
  */
 
 /**
- * @defgroup group_KernelService Other useful kernel service
+ * @defgroup group_kernel_service Other useful kernel service
  * @brief other useful service in the kernel
  */
 
 /**
- * @defgroup group_Error Error Code
+ * @defgroup group_error Error Code
  * @brief error code
  *
  * The error code is defined to identify which kind of error occurs. When some
@@ -96,7 +96,7 @@
  */
 
 /**
- * @defgroup group_SystemInit System Initialization
+ * @defgroup group_system_init System Initialization
  *
  * @brief System initialization procedure.
  *

documentation/0.doxygen/2.components.h

@@ -20,7 +20,7 @@
  */
 
 /**
- * @defgroup group_DFS Device Virtual File System
+ * @defgroup group_device_virtual_file_system Device Virtual File System
  *
  * @brief DFS is a virtual file system in RT-Thread RTOS.
  *
@@ -68,7 +68,7 @@
  */
 
 /**
- * @defgroup group_Module Application Module
+ * @defgroup group_module Application Module
  *
  * @brief Application Module is a feature let user to execute application in RT-Thread RTOS.
  *

documentation/0.doxygen/components/filesystem.h

@@ -3,7 +3,7 @@
  */
 
 /**
- * @addtogroup group_DFS
+ * @addtogroup group_device_virtual_file_system
  * @{
  */
 

documentation/0.doxygen/core/ipc.h

@@ -3,7 +3,7 @@
  */
 
 /**
- * @addtogroup group_IPC
+ * @addtogroup group_thread_comm
  * @{
  */
 

documentation/0.doxygen/core/systeminit.h

@@ -3,7 +3,7 @@
  */
 
 /**
- * @ingroup group_SystemInit
+ * @ingroup group_system_init
  *
  * This function will initialize user application.
  *
@@ -14,6 +14,6 @@
 void rt_application_init();
 
 /**
- * @ingroup group_SystemInit
+ * @ingroup group_system_init
  */
 void rt_system_heap_init(void* begin_addr, void* end_addr);

documentation/0.doxygen/core/thread.h

@@ -3,7 +3,7 @@
  */
 
 /**
- * @addtogroup group_Thread
+ * @addtogroup group_thread_management
  * @{
  */