Use dispatch proxy

[maciejw]

Hello, what do you think about moving from castle dynamic proxy to built in DispatchProxy class, have you considered it when you started this project?
I did few minor upgrades also, like migrate test project to sdk proj, or converted test to xunit since this is default choice in aspnetcore projects.
I also bumped version to 2.0.0 since DispatchProxy requires net461.

I've used typed factories in castle and I think its cool idea, it would be cool to add to https://github.com/aspnet/Extensions

[msftclas]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

❌ maciejw sign now
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[maciejw]

BTW this license/cla Pending — Contributor License Agreement is not signed yet. does not work properly, I've signed it.

[DaveRMaltby]

@maciejw, this PR looks really good. Would love it, if it got merged. Any chance that you might try again at signing the agreement?