REST: incremental compilation support

[ddworak]

As it is, the incremental compiler cannot detect that a change in the interface trait should trigger a macro rerun on the DefaultServerREST, since it's in a different file.

This can be done by expanding relevant macros in the companion object of the RPC trait, as in RPCCompanion (which is not currently supported by io.udash.rest.DefaultRESTFramework).

[ghik]

Related: AVSystem/scala-commons#72

[ddworak]

I think uberpc solved this - let's just update g8 and guide.

[ddworak]

#225