Setup Mergify (#404)
Setup Mergify (#404)

This PR sets up Mergify (mergify.io) bot so that PRs can be merged
automatically after the CI checks are all green.  I set up branch
protection rule in the GitHub web UI
https://github.com/JuliaPy/pyjulia/settings/branches
to list the CIs to be checked by the bot.
JuliaLang/pyjulia,JuliaPy/pyjulia,JuliaPy/pyjulia