move from appveyor into github actions build

[unitycoder]

• 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

[unitycoder]

also would be nice to feed that version number into build (i guess could run script to replace placeholder in some c# script, with that github.run_number value?)
#130

[unitycoder]

added github actions, will look into versio number later

[unitycoder]

actually still need to fix the release infos, should display those commits at least..

now:

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before: (appveyor)