CI on AppVeyor?

[tueda]

Maybe another continuous integration with another compiler in completely different environment would be nice to check the completeness and portability of FORM. A prototype by CMake + MSVS on AppVeyor for Windows: https://github.com/tueda/form/tree/appveyor.

The test suite assumes a POSIX environment and so currently doesn't work on (pure) Windows.