Add new package finch-generic

[vkostyukov]

I think it makes sense to provide finch-generic covering generic derivations on endpoints in Finch. As for today we can build endpoints from query string params (we used to build request readers in the same way):

val e = Endpoint.derive[User].fromParams

I think I'm in favor of Circe-style API for this:

import io.finch.generic._

val e: Endpoint[User] = deriveFromParams[User] // or simiar

Would be also nice to support derivation from path segments.

[teodimoff]

+1