• Add tests for plugin decorators.
• Allow library users to properly cleanup the event loop.
• Expose the asyncio event loop as nvim.loop.
• MsgpackStream: fix typos.

Also a close() method is added on Neovim session objects. When used as
a library for externally connecting to a nvim instance (i.e. not rplugins),
it is recommended to call the close() method on the session object when it is
not needed anymore.

Signed-off-by: Federico Damián Schonborn <federicodamiansch@gmail.com>

nvim +CheckHealth reports the Python 2 and 3 clients are updated and working correctly.