[HUST CSE][document] Fix some comments, invalid grouping commands and warnings in Doxygen.

将Doxygen输入文件（由Doxyfile中的INPUT定义）中的失效Doxygen分组指令（如/*@*/和/*@}*/）更改为有效的分组指令（如/**@*/和/**@}*/）；（此处只对INPUT中的文件做了修改，bsp目录下和libcpu目录下存在近万个失效的Doxygen分组指令，但由于不作为文档的输入文件且这些文件过于庞大老旧，没有对这些文件中的无效指令做修改）
将图片文件统一放入了images目录下；
修改了Doxyfile和部分Doxygen注释，使得Doxyfile能够定位到新的代码路径且不受重复实现的影响；
解决了一些注释中的参数名不匹配、参数多余/缺失等问题。

documentation/doxygen/thread.h

@@ -0,0 +1,89 @@
+/*
+ * This file is only used for doxygen document generation.
+ */
+
+/**
+ * @addtogroup Thread
+ * @{
+ */
+
+/**
+ * @brief This function will handle IPI interrupt and do a scheduling in system.
+ *
+ * @param vector is the number of IPI interrupt for system scheduling.
+ *
+ * @param param is not used, and can be set to RT_NULL.
+ *
+ * @note this function should be invoke or register as ISR in BSP.
+ *
+ * @note this function is only implemented in scheduler_mp.c.
+ */
+void rt_scheduler_ipi_handler(int vector, void *param);
+
+/**
+ * @brief This function will perform one scheduling. It will select one thread
+ *        with the highest priority level in global ready queue or local ready queue,
+ *        then switch to it.
+ *
+ * @note this function is implemented in both scheduler_up.c and scheduler_mp.c.
+ */
+void rt_schedule(void);
+
+/**
+ * @brief This function checks whether a scheduling is needed after an IRQ context switching. If yes,
+ *        it will select one thread with the highest priority level, and then switch
+ *        to it.
+ *
+ * @param context is the context to be switched to.
+ *
+ * @note this function is only implemented in scheduler_mp.c.
+ */
+void rt_scheduler_do_irq_switch(void *context);
+
+/**
+ * @brief This function will insert a thread to the system ready queue. The state of
+ *        thread will be set as READY and the thread will be removed from suspend queue.
+ *
+ * @param thread is the thread to be inserted.
+ *
+ * @note  Please do not invoke this function in user application.
+ *
+ * @note this function is implemented in both scheduler_up.c and scheduler_mp.c.
+ */
+void rt_schedule_insert_thread(struct rt_thread *thread);
+
+/**
+ * @brief This function will remove a thread from system ready queue.
+ *
+ * @param thread is the thread to be removed.
+ *
+ * @note  Please do not invoke this function in user application.
+ *
+ * @note this function is implemented in both scheduler_up.c and scheduler_mp.c.
+ */
+void rt_schedule_remove_thread(struct rt_thread *thread);
+
+/**
+ * @brief This function will lock the thread scheduler.
+ *
+ * @note this function is implemented in both scheduler_up.c and scheduler_mp.c.
+ */
+void rt_enter_critical(void);
+
+/**
+ * @brief This function will unlock the thread scheduler.
+ *
+ * @note this function is implemented in both scheduler_up.c and scheduler_mp.c.
+ */
+void rt_exit_critical(void);
+
+/**
+ * @brief Get the scheduler lock level.
+ *
+ * @return the level of the scheduler lock. 0 means unlocked.
+ *
+ * @note this function is implemented in both scheduler_up.c and scheduler_mp.c.
+ */
+rt_uint16_t rt_critical_level(void);
+
+/**@}*/