add hello module

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@593 bbd45198-f89e-11dd-88c7-29a3b14d5316

components/hello/SConscript

+Import('env')
+
+src = ('hello.c')
+
+obj = env.Object(src)
+
+Return('obj')
+

components/hello/hello.c

+#include <rtthread.h>
+
+void hello()
+{
+    rt_kprintf("Hello RT-Thread\n");
+}