A few more fixes

[AnomalRoil]

• Always expose the ErrUnsupported error, so that Go programs can compare errors with it.
• It seems gen2gbrain/shm does not support s390x and ppc64le architecture, so let's add them to the unsupported ones

Also, would you consider:

• enabling issues on this Github repo?
• tagging a release v0.0.1 or something similar? This would make using Go modules easier with this.

[ZeoWorks]

Hi, what about desktop duplication API for W8+? Would this ever be supported? It's much faster. :) Thanks.

[PhanSon95]

Do you have any suggestion for screenshot on wayland ubuntu?

[crazyoptimist]

Thank you for your great work, @kbinani. I understand you do not have much bandwidth to handle issues in this repo. However, I wanted to ask if you have any plan to support Wayland. Any reply would be much appreciated. Thanks!