Add appveyor.yml.
Add appveyor.yml.

ploeh/FsCheck,ErikSchierboom/FsCheck,sideeffffect/FsCheck,cloudRoutine/FsCheck,fscheck/FsCheck,fscheck/FsCheck,jhamm/FsCheck,paulyoung/FsCheck,fsharp/FsCheck,cloudRoutine/FsCheck,paulyoung/FsCheck