Changelog:
===========
- #384: PackageMetadata now stipulates an additional get method allowing for
easy querying of metadata keys that may not be present.
- #428: packages_distributions now honors packages and modules with Python
modules that not .py sources (e.g. .pyc, .so).
- #434: Expand protocol for PackageMetadata.get_all to match the upstream
implementation of email.message.Message.get_all in python/typeshed#9620.
Signed-off-by: Wang Mingyu <wangmy@fujitsu.com> Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>