Add Change_Interval example

Add Change_Interval example to demonstrate how to change the Timer Interval on-the-fly.

Author: khoih-prog

README.md

@@ -325,6 +325,7 @@ void setup()
  5. [TimerInterruptTest](examples/TimerInterruptTest)
  6. [TimerInterruptLEDDemo](examples/TimerInterruptLEDDemo)
  7. [FakeAnalogWrite](examples/FakeAnalogWrite)
+ 8. [Change_Interval](examples/Change_Interval)
 
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