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. 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)
3. Add examples [multiFileProject](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](khoih-prog/ESP8266_PWM#1 (comment))
5. Optimize library code by using `reference-passing` instead of `value-passing`
6. Update examples accordingly

Author: khoih-prog

README.md

@@ -54,6 +54,23 @@
 ---
 ---
 
+### Important Change from v1.2.0
+
+Please have a look at [HOWTO Fix `Multiple Definitions` Linker Error](#howto-fix-multiple-definitions-linker-error)
+
+As more complex calculation and check inside ISR are introduced from v1.2.0, there are consequences as follows
+
+- using min 30uS and max 8 PWM channels
+
+```
+// Don't change these numbers to make higher Timer freq. System can hang
+#define HW_TIMER_INTERVAL_US        30L
+#define HW_TIMER_INTERVAL_FREQ      33333L
+```
+
+You certainly can modify to use better values according to your board and use-case, just remember to test and reverse to conservative values if crash happens.
+
+
 ### Why do we need this [SAMDUE_Slow_PWM library](https://github.com/khoih-prog/SAMDUE_Slow_PWM)
 
 ### Features