v1.3.0 to fix multiple-definitions linker error

### Releases v1.3.0

1. Fix `multiple-definitions` linker error. Drop `src_cpp` and `src_h` directories
2. Add example [multiFileProject](examples/multiFileProject) to demo for multiple-file project.
3. Optimize library code by using `reference-passing` instead of `value-passing`
4. Update all examples

Author: khoih-prog

README.md

@@ -17,6 +17,7 @@
   * [Why using ISR-based Hardware Timer Interrupt is better](#why-using-isr-based-hardware-timer-interrupt-is-better)
   * [Currently supported Boards](#currently-supported-boards)
   * [Important Notes about ISR](#important-notes-about-isr)
+* [Changelog](changelog.md) 
 * [Prerequisites](#prerequisites)
 * [Installation](#installation)
   * [Use Arduino Library Manager](#use-arduino-library-manager)