Added github actions workflows

[cmaglie]

This is based on what we do in the arduino-cli, I've re-used part of the workflows and slightly changed DistTasks.yml:

• using go 1.15.8 (I checked for 1.16 but it's not yet in the docker image)
• renamed the build folder from _linux_amd32 to _linux_386 (just a temp folder make-up doesn't affect the final artifacts)

[cmaglie]

Also I've refreshed the generated win32 syscalls with the latest mksyscall, not strictly related to this PR but I needed it to produce a test build.