Create a separate Spec artifact

[keilw]

For a future version, we should create a separate "spec" artifact similar to https://github.com/eclipse-ee4j/websocket-api.

[stokito]

what is a difference with api artifact?

[keilw]

Nothing but the API build is not polluted and slowed down when you don't want to build the spec every time ;-)