More targeted dotnet version✨ [FEATURE]

[Dimkar3000]

Summary

This library could easily target more that .net5. I successfully tested this in in core3.1 without any problem. Having taken a look in this library I see no reason for this not to work in any version of donet. This could be done by a simple edit in the csproj files. I have personally tested 3.1 so anything newer should be ok.

Advantage

Makes this project usable independently of c# version. The Timers api works since core2.0 and .net standard 2.0.