Replace most ToServer instances with a single overlappable instance

[ambroslins]

We can construct a server from every route. However this requires UndecidableInstances and a OVERLAPPABLE pragma.

Not sure if this is actually better, but it does mean we have to don´t have to define extra instances for the ToServer class.

I will just leave this here. Feel free to close it if you don´t like it.

[anton-k]

This is interesting. I need to try it out with examples. As sometimes OVERLAPPABLE-code compiles on the library level. But produces errors on the level of the user code.

[ambroslins]

Yes, I am also not sure whether this might cause problems down the line. I just saw that a instance like this should be possible because the other instances are basically all the same.

Btw. I am really excited about this project and also looking forward to contributing. So if you need help with anything just let me know.

[anton-k]

We an also remove that instance from the file mig-extra/src/Mig/Extra/Server/Json.hs

[anton-k]

Thank you for support and help poposal.
I keep file todo.md of the things that I'd like to do next. Maybe it would be worth while to convert them to issues.
If you are interested in contribution you can also take some of those items. Some of them are small some of them are really big.

[anton-k]

All examples compile. i think we can merge it.

[anton-k]

thanks for fix! Merged