##Changes
###0.8.17
- (not support anymore) implicit dereferencing, which is conflict with 'relative file reference'
"definitions":{ "User":{ }, "AuthorizedUser":{ "$ref": "User" --> deferenced to "#/definitions/User" } }
- NEW relative file reference
"definitions":{ "User": { "$ref": "other_folder/User.json" } }
- NEW the root object of external documents can be any object (need to be an Swagger/PathItem object before this version)
- fix issue: use 'netloc' only when no host provided.