Remove Appveyor and add Azure build status branch protection

[gusmith]

Currently, a commit can be merged if it receives the appveyor build status continuous-integration/appveyor/pr.
But we are not replacing appveyor with Azure Build pipeline (merged in master with PR #262), so we should change the branch protection and change the appveyor configuration not to build the project anymore.

[hardbyte]

I've added the Azure checks and removed the requirement for appveyor:

This issue is therefore to remove the appveyor configuration then?

[MehdiGol]

Hello, Can I ask a question?
Why did you migrate from AppVeyor to Azure?

[gusmith]

Hi @MehdiGol
I can only mentioned what I remember, which is not that much as it happened a few years ago now, but at the time, Azure had really great offers for open source projects to run CI and CD (number of parallel jobs, time to get a worker, etc).
From memory, we found that AppVeyor was quite slow (e.g. #121) but I do not remember well the details... was it time to get a worker? Was it the worker resources which were a bit small?
Hoping that help.