v1.2.0 to fix `multiple-definitions` linker error, to improve accuracy, DutyCycle to be optionally updated at the end current PWM period instead of immediately, etc.

Releases v1.2.0

1. Fix multiple-definitions linker error. Drop src_cpp and src_h directories
2. 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
3. Add examples multiFileProject to demo for multiple-file project
4. Improve accuracy by using double, instead of uint32_t for dutycycle, period. Check Change Duty Cycle #1
5. Optimize library code by using reference-passing instead of value-passing
6. Update examples accordingly