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/0.basicdef.h

@@ -0,0 +1,14 @@
+/*
+ * This file is only used for doxygen document generation.
+ */
+
+/**
+ * @defgroup group_BasicDef Basic Definitions
+ *
+ * @brief Basic data type in RT-Thread RTOS.
+ *
+ * These are the basic definitions which used in RT-Thread RTOS. In general,
+ * RT-Thread kernel uses its own definition of the basic data types, such as
+ * rt_uint32_t, rt_uint8_t, etc., which does not depend on the compiler or
+ * architecture.
+ */