Close Multi timers atexit. Add 1.6 CI #325

Job	Run time
Julia 1.3 - ubuntu-latest - x64 - pull_request	28s
Julia 1.3 - ubuntu-latest - x86 - pull_request	39s
Julia 1.3 - macos-latest - x64 - pull_request	3m 1s
Julia 1.3 - windows-latest - x64 - pull_request	8m 39s
Julia 1.3 - windows-latest - x86 - pull_request	7m 32s
Julia 1.6 - ubuntu-latest - x64 - pull_request	37s
Julia 1.6 - ubuntu-latest - x86 - pull_request	40s
Julia 1.6 - macos-latest - x64 - pull_request	1m 25s
Julia 1.6 - windows-latest - x64 - pull_request	9m 3s
Julia 1.6 - windows-latest - x86 - pull_request	10m 15s
Julia 1 - ubuntu-latest - x64 - pull_request	2m 29s
Julia 1 - ubuntu-latest - x86 - pull_request	2m 23s
Julia 1 - macos-latest - x64 - pull_request	2m 42s
Julia 1 - windows-latest - x64 - pull_request	3m 1s
Julia 1 - windows-latest - x86 - pull_request	3m 10s
Julia nightly - ubuntu-latest - x64 - pull_request	2m 8s
Julia nightly - ubuntu-latest - x86 - pull_request	2m 20s
Julia nightly - macos-latest - x64 - pull_request	2m 53s
Julia nightly - windows-latest - x64 - pull_request	2m 37s
Julia nightly - windows-latest - x86 - pull_request	3m 0s
	1h 9m 2s

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