Add Native Platform for http4s, http4s-stir

[luksow]

This is currently blocked by the release of enumeratum and http4s for Scala Native 0.5.x.

In case http4s is released for Scala Native 0.5.x, to prevent this from being blocked any further, we should consider rewriting tests which depends on enumeratum support to native Scala 2's enums or so.

See: #389 for reference.

[luksow]

enumeratum and circe added in 3fe7d98

http4s and http4s-stir currently don't have a release for SN 0.5