Version 5.0.0 - The era of async/await

Changes

The big change is that the background update job is now running as an ordinary Python coroutine.
If you use Gaphas, make sure you set up the GLib asyncio event loop.

The decorators (g_async, nonrecursive) are gone.

🚀 Features

• Use asyncio for view updates @amolenaar (#829)

Thanks again to @amolenaar and @danyeaw! 🎉