feat: update deps to version 3.1.0

chore: update deps for .NET-Core 3.0

feat: update libraries to .NET-Standard 2.1 and add support for .NET-…

…Core 3 / .NET-Standard 2.1

Remove redundant abstraction of `DbContext` and add new functionalities

* Removes `GenericRepositoryContext` and uses `DbContext`
* Adds new APIs to load results into projections
* Adds new APIs to add many items at once
* Add new tests
* Update samples and changelog

Closes #1 and #2

Release 2.2.4

Version 2.2.2

Update EntityframeworkCore to version 2.2.1 and adjust changelog

update packages and prepare release 2.1.2

version 2.2.0

Version 2.1.0, add matching functionality

Version 1.3.0 / Paging-Repository