devel/py-yamlloader: New port

This module provides loaders and dumpers for PyYAML.

Currently, an OrderedDict loader/dumper is implemented, allowing to keep
items order when loading respective dumping a file from/to an
OrderedDict.

(Python 3.8+: Also regular dicts are supported and are the default items
to be loaded to. As of Python 3.7 preservation of insertion order is a
language feature of regular dicts.)

This project was originally mirrored from "yamlordereddict" and contains
several improvements including automated testing and the much faster
C-versions of the Loaders/Dumpers.