Typing stubs for PyYAML

This is a PEP 561 type stub package for the PyYAML package. It can be used by type-checking tools like mypy, PyCharm, pytype etc. to check code that uses PyYAML. The source for this package can be found at https://github.com/python/typeshed/tree/master/stubs/PyYAML. All fixes for types and metadata should be contributed there. See https://github.com/python/typeshed/blob/master/README.md for more details.