doxygen: re-org module groups (#10197)

Match the organization of modules (groups) with
that of user guide.

Preliminary arrangement. This patch is just a
framework arrangement. Details need to be continued.

P.S., in this patch, adding numerical prefixes to
the files in documentation/0.doxygen is to meet the
need of displaying sorting in HTML pages.

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

documentation/0.doxygen/1.core.h

@@ -0,0 +1,142 @@
+/*
+ * This file is only used for doxygen document generation.
+ */
+
+/**
+ * @defgroup group_kernel_core Kernel
+ *
+ * Core of RT-Thread, see @ref page_kernel_core for more details.
+ */
+
+/**
+ * @addtogroup group_kernel_core
+ * @{
+ */
+
+/**
+ * @defgroup group_KernelObject Kernel Object Management
+ * @brief See @ref section_kernel_object_model
+ *
+ * The Kernel object system can access and manage all of the kernel objects.
+ *
+ * Kernel objects include most of the facilities in the kernel:
+ * - thread
+ * - semaphore and mutex
+ * - event/fast event, mailbox, messagequeue
+ * - memory pool
+ * - timer
+ * @image html Kernel_Object.png "Figure 2: Kernel Object"
+ * @image rtf  Kernel_Object.png "Figure 2: Kernel Object"
+ *
+ * Kernel objects can be static objects, whose memory is allocated in compiling.
+ * It can be dynamic objects as well, whose memory is allocated from system heaps
+ * in runtime.
+ */
+
+/**
+ * @defgroup group_Thread Thread Management
+ * @brief See @ref page_thread_management
+ */
+
+/**
+ * @defgroup group_Clock Clock and Timer Management
+ * @brief See @ref page_clock_management
+ */
+
+/**
+ * @defgroup group_IPC Inter-Thread Communication
+ * @brief See @ref page_thread_comm
+ */
+
+/**
+ * @defgroup group_MM Memory Management
+ * @brief memory management for memory pool and heap memory
+ *
+ * RT-Thread operating system supports two types memory management:
+ * - Static memory pool management
+ * - Dynamic memory heap management.
+ *
+ * The time to allocate a memory block from the memory pool is determinant. When
+ * the memory pool is empty, the allocated thread can be blocked (or immediately return,
+ * or waiting for sometime to return, which are determined by a timeout parameter).
+ * When other thread releases memory blocks to this memory pool, the blocked thread is
+ * wake up.
+ *
+ * There are two methods in dynamic memory heap management, one is used for small memory,
+ * such as less than 1MB.  Another is a SLAB like memory management, which is suitable
+ * for large memory system. All of them has no real-time character.
+ */
+
+/**
+ * @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
+ * is introduced.
+ *
+ * The hooks are a series of routines, which are invoked in some special checkpoints.
+ * The hook routines include:
+ * - object hook, invoked at object created, deleted, taken and put etc.
+ * - scheduler hook, invoked at thread switch and idle thread loop.
+ * - memory hook, invoked when allocate or free memory block.
+ * - timer hook, invoked when timer is timeout.
+ */
+
+/**
+ * @defgroup group_KernelService Other useful kernel service
+ * @brief other useful service in the kernel
+ */
+
+/**
+ * @defgroup group_Error Error Code
+ * @brief error code
+ *
+ * The error code is defined to identify which kind of error occurs. When some
+ * bad things happen, the current thread's errno will be set.
+ */
+
+/**
+ * @defgroup group_SystemInit System Initialization
+ *
+ * @brief System initialization procedure.
+ *
+ * When RT-Thread operating system starts up, the basic operating system facility
+ * initialization routines must be invoked.
+ *
+ * The suggested initialization sequence is:
+ *
+ * - initialize device hardware
+ * rt_hw_board_init();
+ *
+ * User can put the low level hardware initialization in this function, such as
+ * DDR memory setting, pinmux setting, console device setting etc.
+ *
+ * - show version
+ * rt_show_version();
+ *
+ * - initialize timer system
+ * rt_system_timer_init();
+ *
+ * - initialize system heap memory
+ * rt_system_heap_init(__bss_end, __end_of_memory);
+ *
+ * - initialize module system
+ * rt_system_module_init();
+ *
+ * - initialize scheduler system
+ * rt_system_scheduler_init();
+ *
+ * - initialize application
+ * rt_application_init();
+ *
+ * - initialize system timer thread
+ * rt_system_timer_thread_init();
+ *
+ * - initialize idle thread
+ * rt_thread_idle_init();
+ *
+ * - start scheduler
+ * rt_system_scheduler_start();
+ */
+
+/**@}*/