Setup continuous integration appveyor & azure

[upupming]

To make future test and release more productive, I have already added and tested CI on appveyor and azure pipelines, both are okay on my own fork and all branches. See artifact built using the source of my fork on appveyor and azure pipelines. And GitHub show as below:

I think azure is more promising as it will test on different platforms (linux, windows, and macOS). But appveyor is much faster.

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However, it seems that I don't have sufficient privilege to set up these environments to PicGo/vs-picgo, could you please help?

Steps you may need to take:

1. Merge this PR to master.
2. Goto https://ci.appveyor.com/project/picgo/vs-picgo and https://azure.microsoft.com/en-us/services/devops/pipelines/ to properly authenticate this repo.
3. Start a build and see if the artifact is built successfully, and also test if commits on dev branch will be automatically built.

Thanks for your patience in advance!