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. Improve accuracy by using `float`, instead of `uint32_t` for `dutycycle`. Check [Change Duty Cycle #1](khoih-prog/ESP8266_PWM#1 (comment))
3. DutyCycle to be optionally updated at the end current PWM period instead of immediately. Check [DutyCycle to be updated at the end current PWM period #2](khoih-prog/ESP8266_PWM#2)
4. Optimize library code by using `reference-passing` instead of `value-passing`
5. Add example [multiFileProject](examples/multiFileProject) to demo for multiple-file project
6. Update examples accordingly

Author: khoih-prog

README.md

@@ -288,8 +288,12 @@ void setup()
 // Don't define _PWM_LOGLEVEL_ > 0. Only for special ISR debugging only. Can hang the system.
 #define _PWM_LOGLEVEL_      4
 
-#define USING_MICROS_RESOLUTION       true    //false 
+#define USING_MICROS_RESOLUTION       true    //false
 
+// Default is true, uncomment to false
+//#define CHANGING_PWM_END_OF_CYCLE     false
+
+// To be included only in main(), .ino with setup() to avoid `Multiple Definitions` Linker Error
 #include "RP2040_Slow_PWM.h"
 
 #include <SimpleTimer.h>              // https://github.com/jfturcot/SimpleTimer