ci: Remove use of AppVeyor

[mloskot]

Motivation

Following @sdebionne question in #596 (comment) I think it's time to get rid of AppVeyor and get closer to the overall Boost trend to switch to GitHub Actions. We're still having some support from Azure Pipelines, however it's different (or not) from the GA, who knows.

State

Our GA+AZ:

gil/.github/workflows/ci.yml

Lines 149 to 160 in 7dd6120

	- toolset: msvc-14.1
	cxxstd: "14,17,latest"
	addrmd: 32,64
	os: windows-2016
	- toolset: msvc-14.2
	cxxstd: "14,17,latest"
	addrmd: 32,64
	os: windows-2019
	- toolset: gcc
	cxxstd: "11,14,17,2a"
	addrmd: 64
	os: windows-2019

gil/.azure-pipelines.yml

Line 56 in 7dd6120

- job: 'win2016_vs2017_cxx14_cmake'

gil/.azure-pipelines.yml

Line 73 in 7dd6120

- job: 'win2016_vs2017_cxx17_cmake'

is covering most of our AV:

gil/.appveyor.yml

Lines 20 to 63 in 7dd6120

	- TOOLSET: msvc-14.0
	ARCH: x86_64
	VARIANT: debug
	CXXSTD: 11
	TEST_HEADERS: 1
	APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
	- TOOLSET: msvc-14.0
	ARCH: x86_64
	VARIANT: release
	CXXSTD: 11
	TEST_HEADERS: 1
	APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
	- TOOLSET: msvc-14.1
	ARCH: x86_64
	VARIANT: debug
	CXXSTD: 14
	TEST_HEADERS: 1
	APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
	- TOOLSET: msvc-14.1
	ARCH: x86_64
	VARIANT: release
	CXXSTD: 14
	APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
	- TOOLSET: msvc-14.1
	ARCH: x86
	VARIANT: debug
	CXXSTD: 14
	APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
	- TOOLSET: msvc-14.1
	ARCH: x86
	VARIANT: release
	CXXSTD: 14
	APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
	- TOOLSET: msvc-14.1
	ARCH: x86_64
	VARIANT: debug
	CXXSTD: 17
	TEST_HEADERS: 1
	APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
	- TOOLSET: msvc-14.1
	ARCH: x86_64
	VARIANT: release
	CXXSTD: 17
	APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017

Future

The only difference being release and debug build variants tested on AV, but that should be easy to add to GA.

[striezel]

We're still having some support from Azure Pipelines, however it's different (or not) from the GA, who knows.

Azure Pipelines is in the process of removing Windows Server 2016 with Visual Studio 2017, so it will no longer be available. See https://devblogs.microsoft.com/devops/hosted-pipelines-image-deprecation/ for more information.

However, Azure seems indeed to be using the same stuff as GitHub Actions, so we are still covered when it comes to MSVC.