Moved the implementation header file to a separate .cpp file

[jjwbruijn]

My project using timers across multiple files wouldn't compile, because the header would pull the same implementation from the different files. I moved the implementation header to a cpp file and removed the bottom #include in ESP32_ISR_Timer.h

[khoih-prog]

Thanks for your PR.

I'm about to convert all the libraries using h-only style into both h-only and standard-cpp to provide an option to people having Multiple Definitions Linker Error

Please have a look at what has been done to other libs such as:

HOWTO Fix Multiple Definitions Linker Error in ESP_WiFiManager
HOWTO Fix Multiple Definitions Linker Error in ESPAsync_WiFiManager
and many more

So I'm sorry I won't merge your PR but will create a new version to give the better options to use either way.

[jjwbruijn]

Thanks for your quick reply and this awesome library! Too bad this means you will always need to perform manual actions after pulling the library using PlatformIO, reducing the user-friendlyness somewhat. But choice is always good :)

[khoih-prog]

you will always need to perform manual actions after pulling the library using PlatformIO, reducing the user-friendlyness somewhat. But choice is always good :)

That's the difficult choice I had to make some time ago, and I decided to go with h-only style because of many benefits, one of them is the permeation of definitions (debug, options, etc.) from the sketch into all the libraries at compile time.

And I still like the current approach after writing many libs using the h-only style, but I still give the options for the standard-cpp style from the feedbacks of libs' users like you.