py37-ruamel @0.16.5, py-ruamel-yaml-clib @0.1: missing clib after split into separate package

[lhaeger (Lothar Haeger)]

C sources have been split into separate package in 0.16.0 and are now missing in the ports tree. With ruamel.yaml updated to versions >0.15 an additional port "py-ruamel-yaml-clib" needs to be created and added as dependency to py-ruamel-yaml until all ports depending on py-ruamel-yaml have their own dependencies checked and updated with py-ruamel-yaml-clib if used.

Please see changelog at ​https://bitbucket.org/ruamel/yaml/src/default/ and ​https://pypi.org/project/ruamel.yaml.clib/ for details

This came up in ​https://trac.macports.org/ticket/58792