Set up appveyor builds

[rpavlik]

AppVeyor appears to be the Travis-CI for Windows. Should get it going.

[malcolmathci]

@rpavlik I see AppVeyor listed next to Travis-CI for the continuous integration checks for my pull request #483. Should this issue still be open?

[gfrolov]

@malcolmathci,
AppVeyor CI check is enabled but setup is not yet complete, because it needs a config file appveyor.yml, which is similar to travis.yml in the root directory, and is used to configure the build. We'd gladly welcome your contribution if you wanted to give it a try.
Here are some references - https://www.appveyor.com/docs/build-configuration/#configuring-build
https://www.appveyor.com/docs/appveyor-yml/

[godbyk]

@mars979 I've done some work for this already in the appveyor branch, but I don't think it's completely functional yet. See my appveyor.yml.

[malcolmathci]

@mars979 @godbyk Thanks for the info. I'll review the docs and resume work on appveyor.yml.

[rpavlik]

Note that while it's listed as a check, it's not currently being enforced for pull requests, only travis is. (since it's not complete)