Fix imprecisse timing on SAMD21

Fixed imprecisse timing on SAMD21 (Arduino Zero). This solves #21. Thanks to @daniel-mohr

Fix ESP32 typo

Fix ESP32 typo

Add compatibility withnew STM32 core versions

Add compatibility with new STM32 core versions. Fixes #16 and #17

Note: Still maintains retrocompatibility with older cores.

Fix ESP32 clearTimer

Fix a bug when using multiple timers (continuous, not at same time) on ESP32.

Fix ESP32 clearTimer

Fix clearTimer functionality on ESP32. Fixes #14

Enhance ESP32 support using OS hardware timer

Enhance ESP32 support using OS hardware timer

Add DigiSpark AVR support

Add DigiSpark AVR support using Timer0 (Timer1 is in use for milis)

STM32 fixes

Add uncommited STM32 fixes

STM32 ST Core fixes

Fixed STM32 ST Core Timers changes - https://github.com/stm32duino/Arduino_Core_STM32

Fixes #12

STM32 fixes

Fixes for STM32 copilers and new ST core releases