Chapter3: power2/3/5 & sleep test worked on k210/qemu based on timer.

user/src/bin/03sleep.rs

@@ -0,0 +1,18 @@
+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate user_lib;
+
+use user_lib::{sys_get_time, sys_yield};
+
+#[no_mangle]
+fn main() -> i32 {
+    let current_timer = sys_get_time();
+    let wait_for = current_timer + 10000000;
+    while sys_get_time() < wait_for {
+        sys_yield();
+    }
+    println!("Test sleep OK!");
+    0
+}