std: Rename sleep, periodic, and oneshot timers to sleep_ms, etc.

Rename io::timer::sleep, Timer::sleep, Timer::oneshot,
Timer::periodic, to sleep_ms, oneshot_ms, periodic_ms. These functions
all take an integer and interpret it as milliseconds.

Replacement functions will be added that take Duration.

[breaking-change]

src/libstd/io/process.rs

@@ -976,7 +976,7 @@ mod tests {
                 assert!(!p.wait().unwrap().success());
                 return
             }
-            timer::sleep(100);
+            timer::sleep_ms(100);
         }
         fail!("never saw the child go away");
     })