Add `Read` instances for names and binder or how to derive it

[ksenia-portu]

Do Read instances don't exist by design choice or it can be somehow derived? Instances for Name a from http://hackage.haskell.org/package/unbound-generics-0.4.0/docs/src/Unbound.Generics.LocallyNameless.Name.html#line-84
and Bind p t from http://hackage.haskell.org/package/unbound-generics-0.4.0/docs/src/Unbound.Generics.LocallyNameless.Bind.html#Bind

[lambdageek]

It's not by design, rather:

• Read instances weren't in Unbound so I didn't add them to unbound-generics
• For most of my own projects using unbound-generics I was not using it for the surface syntax of a language - only for an internal IR. So the Show instances were only for debugging, not for anything user-visible. Consequently I never had a use for Read - the surface languages always used normal parsers (either using happy or using parsec).

I'd accept a PR implementing Read instances, but they would need to be perfect inverses of Show - which I'm not sure is possible because the Show instances omit some information.