Add configuration for CI on Windows
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Add Appveyor configuration to compile and tests on Windows (https://ci.appveyor.com/project/raimis/libxc-udj4h/build/1.0.3/job/yegnt6i8lt2a2h04).
Appveyor has to be activated on the repository to work (https://www.appveyor.com/docs/).
This is a part of Psi4 porting to Windows (https://github.com/psi4/psi4/issues/933)