Spec compliant path parameter handling

[line-o]

Roaster allows path parameters to contain slashes (/).
This is not part of the current spec (OAS 3.0.3).

A rather long discussion can be found here OAI/OpenAPI-Specification#892

For us to still be able to support this very much wanted use-case but still be spec compliant I suggest we implement another extension x-multiSegment as suggested in this comment

[line-o]

If we implement this it will be a breaking change.