Refactored libunshield CMakeLists to build on windows

[twogood]

Create pull request to see if Travis and Appveyor picks it up

[kpyrkosz]

Spent some time digging in appveyor docs and found out how to have separate linux and windows configs in two different yaml files. It is possible to set up the CI for the same repo twice, with different Custom configuration .yml file name file set to .appveyor-windows.yml in first case and .appveyor-linux.yml in second. This is particularly convenient because the build procedure in both cases is diametrally different, splitting into two per-OS configurations makes it more readable and smaller. This is how it looks in practice:
https://ci.appveyor.com/project/kpyrkosz/unshield-windows
https://ci.appveyor.com/project/kpyrkosz/unshield-linux

Notice that the build above (in this PR) is still usint the old script (and even tho it flashes green it is broken).
I've restored your original travis file so it does not contain any of my modifications, the branch is mergable.

[twogood]

Excellent work!!!

Thanks! I'll try to sort this out ASAP but I'm in a busy period right now.

[kpyrkosz]

Any progress? :)

[twogood]

Thank you for the kind reminder @kpyrkosz. Maybe just merge? :)

PS. I heard Travis-ci is closing down their .org and we have to migrate to their .com version...

[kpyrkosz]

Yes, you can merge, is there any obstacle in the way?

[twogood]

Damn, I shouldn't have squashed it, now I get the git blame....