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 feature to select among highest, medium or lowest accuracy for Timers for shortest, medium or longest time
3. Fix reattachInterrupt() bug. Check [bugfix: reattachInterrupt() pass wrong frequency value to setFrequency() #19](khoih-prog/ESP8266TimerInterrupt#19)
4. Add example [multiFileProject](examples/multiFileProject) to demo for multiple-file project
5. Improve accuracy by using `double`, instead of `uint32_t` for `dutycycle`, `period`. Check [Change Duty Cycle #1](#1 (comment))
6. Update examples accordingly

README.md

@@ -31,6 +31,7 @@
   * [ 3. ISR_16_PWMs_Array_Simple](examples/ISR_16_PWMs_Array_Simple)
   * [ 4. ISR_Changing_PWM](examples/ISR_Changing_PWM)
   * [ 5. ISR_Modify_PWM](examples/ISR_Modify_PWM)
+  * [ 6. multiFileProject](examples/multiFileProject)
 * [Example ISR_16_PWMs_Array_Complex](#Example-ISR_16_PWMs_Array_Complex)
 * [Debug Terminal Output Samples](#debug-terminal-output-samples)
   * [1. ISR_16_PWMs_Array_Complex on ESP8266_NODEMCU_ESP12E](#1-ISR_16_PWMs_Array_Complex-on-ESP8266_NODEMCU_ESP12E)