Replaced Appveyor with GitHub actions #5

Job	Run time
build (TestCore, windows-2022, 10.0.x)	2m 23s
build (TestCore, ubuntu-22.04, 8.0.x, --netcore=net8.0)	1m 23s
build (TestCore, macos-15, 8.0.x, --netcore=net8.0)	1m 14s
build (TestCore, windows-2022, 8.0.x, --netcore=net8.0)	2m 46s
build (TestCore, ubuntu-22.04, 10.0.x)	1m 11s
build (Test, windows-2022, 10.0.x)	2m 31s
build (TestCore, macos-15, 10.0.x)	1m 18s
	12m 46s

Provide feedback