v1.1.0 for new PWM_manual example, etc.

### Releases v1.1.0

1. Add example [PWM_manual](https://github.com/khoih-prog/AVR_PWM/examples/PWM_manual) to demo how to correctly use PWM to generate waveform. Check [About DCValue in setPWM_manual #2](#2)
2. Add function `setPWM_DCPercentage_manual()` to facilitate the setting PWM DC manually by using DCPercentage, instead of absolute DCValue depending on varying PWMPeriod
3. Catch low frequency error and use lowest permissible frequency

Author: khoih-prog

changelog.md

@@ -29,7 +29,7 @@
 
 1. Add example [PWM_manual](https://github.com/khoih-prog/AVR_PWM/examples/PWM_manual) to demo how to correctly use PWM to generate waveform. Check [About DCValue in setPWM_manual #2](https://github.com/khoih-prog/AVR_PWM/discussions/2)
 2. Add function `setPWM_DCPercentage_manual()` to facilitate the setting PWM DC manually by using DCPercentage, instead of absolute DCValue depending on varying PWMPeriod
-3. Catch low frequency error and use lowest permissile frequency
+3. Catch low frequency error and use lowest permissible frequency
 
 ### Releases v1.0.1