Dependency on the Anaconda-specific, non-upstream ruamel_yaml variant

[mbargull]

I'm currently looking at what packages on conda-forge have a dependency on the non-maintained ruamel_yaml package.

I'd like us to remove ruamel_yaml from future builds.
To be able to do this with good conscience, it'd be good if ommprotocol could be updated to use upstream ruamel.yaml always.

ommprotocol.io already uses a try: ... except ImportError: ... construct with ruamel.yaml as a fallback, which is good.
It would, however, need ruamel.yaml<0.18 since it uses the deprecated top-level ruamel.yaml.load function.
(Details for the upstream change can be read at https://pypi.org/project/ruamel.yaml/0.18.3/ .)

Would it be possible for you to update ommprotocol.io to be compatible with ruamel.yaml=0.18 and change the dependency from ruamel_yaml to ruamel.yaml?

xref: conda-forge/ommprotocol-feedstock#1