v1.2.0 to fix multiple-definitions linker error

### Releases v1.2.0

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

library.properties

@@ -3,7 +3,7 @@ version=1.2.0
 author=Khoi Hoang <[email protected]>
 maintainer=Khoi Hoang <[email protected]>
 sentence=This library enables you to use Interrupt from Hardware Timers on RP2040-based boards such as RASPBERRY_PI_PICO
-paragraph=These RPI_PICO_TimerInterrupt Hardware Timers, using Interrupt, still work even if other functions are blocking. Moreover, they are much more precise (certainly depending on clock frequency accuracy) than other software timers using millis() or micros(). That's mandatory if you need to measure some data requiring better accuracy. It now supports 16 ISR-based Timers, while consuming only 1 Hardware Timer. Timers' interval is very long (ulong millisecs). The most important feature is they're ISR-based Timers. Therefore, their executions are not blocked by bad-behaving functions or tasks. This important feature is absolutely necessary for mission-critical tasks.
+paragraph=These RPI_PICO_TimerInterrupt Hardware Timers, using Interrupt, still work even if other functions are blocking. Moreover, they are much more precise (certainly depending on clock frequency accuracy) than other software timers using millis() or micros(). That is mandatory if you need to measure some data requiring better accuracy. It now supports 16 ISR-based Timers, while consuming only 1 Hardware Timer. Timers interval is very long (ulong millisecs). The most important feature is they are ISR-based Timers. Therefore, their executions are not blocked by bad-behaving functions or tasks. This important feature is absolutely necessary for mission-critical tasks.
 category=Device Control
 url=https://github.com/khoih-prog/RPI_PICO_TimerInterrupt
 architectures=rp2040