move from appveyor into github actions build

create github actions config (build & release)
build only main branch or on "#build" message only?
give automatic version number to release (like appveyor did? or start from same counter value at least?) ** takes current version number from yaml : github.run_number
remove appveyor files and setup *or can leave as backup
remove appveyor build status badge
add github build status badge
add commits info to build description *only shows last commit now..
add timestamp to build description text, since github doesn't show exact build date
dont show failed build banner, if didnt make build

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