[Feat] add CI / github actions to this repo.

[Green-Sky]

For compiling and ideally for testing all the different platforms. maybe copy the ones from llama.cpp

[koogle]

@Green-Sky I assume this can be closed now that #247 is merged

[Green-Sky]

Hm maybe, but I wanted it to be more thorough, eg sanitizers. Also it should build example binaries. Also it only build on ubuntu and macos right now. :) I am going to leave this open for now. BUT the ggml projects are being refactored/restructured somewhat, so we might see /ggml /llama.cpp consolidation or other things, that would make this obsolete...