examples/hwapi: Add example for machine.time_pulse_us().

examples/hwapi/button_reaction.py

@@ -0,0 +1,19 @@
+import utime
+import machine
+from hwconfig import LED, BUTTON
+
+# machine.time_pulse_us() function demo
+
+print("""\
+Let's play an interesting game:
+You click button as fast as you can, and I tell you how slow you are.
+Ready? Cliiiiick!
+""")
+
+while 1:
+    try:
+        delay = machine.time_pulse_us(BUTTON, 1, 10*1000*1000)
+        print("You are as slow as %d microseconds!" % delay)
+    except OSError:
+        print("Well, you're *really* slow")
+    utime.sleep_ms(10)