Wrapper: use generics

[gucio321]

fix #55

[gucio321]

I'm going to do the same for slice types

[gucio321]

and one more note:
fore some reasons, IDEs thinks the conversions in the code as build issues (e.g. goland: https://youtrack.jetbrains.com/issue/GO-14048/false-build-failure-with-generics) but it compiles normally

[gucio321]

I'm going to do the same for slice types

well nevermind - it is not used the way I tought it is 😄

[eliasdaler]

Please don't use PR's for drafts - develop in your own fork. It pollutes notifications - I'm only interested in final code.

[gucio321]

it is already ready for review