Add config file for azure pipelines

As an experiment we will run azure pipelines alongside travis ci until the next major release. If it turns to out be more convenient then we will switch permanently. Note: deployment stage is not configured yet. Also there is potential to simplify the config using templates.

azure-pipelines.yml

@@ -0,0 +1,61 @@
+trigger:
+  branches:
+    include:
+    - develop
+    - release-*
+    - hotfix-*
+  tags:
+    include:
+    - '*'
+
+stages:
+- stage: test
+  displayName: 'Build & Test'
+  jobs:
+  - job: macos
+    strategy:
+      matrix:
+        macosSwift50:
+          imageName: 'macOS-10.14'
+          DEVELOPER_DIR: '/Applications/Xcode_10.3.app'
+        macosSwift51:
+          imageName: 'macOS-10.15'
+          DEVELOPER_DIR: '/Applications/Xcode_11.3.1.app'
+        macosSwift52:
+          imageName: 'macOS-10.15'
+          DEVELOPER_DIR: '/Applications/Xcode_11.4.app'
+    pool:
+      vmImage: $(imageName)
+    steps:
+    - script: |
+        brew update
+        ./utils.py ci install-macos
+      displayName: 'Install'
+    - script: ./utils.py prepare-workspace macos
+      displayName: 'Prepare Workspace'
+    - script: ./utils.py ci script-macos
+      displayName: 'Build & Test'
+    - script: swift build -c release # Check Release build just in case.
+      displayName: 'Build SPM Release'
+  - job: linux
+    strategy:
+      matrix:
+        linuxSwift50:
+          imageName: 'ubuntu-18.04'
+          SWIFT_VERSION: '5.0'
+        linuxSwift51:
+          imageName: 'ubuntu-18.04'
+          SWIFT_VERSION: '5.1'
+        linuxSwift52:
+          imageName: 'ubuntu-18.04'
+          SWIFT_VERSION: '5.2'
+    pool:
+      vmImage: $(imageName)
+    steps:
+    - script: ./utils.py ci install-linux
+      displayName: 'Install'
+    - script: ./utils.py ci script-linux
+      displayName: 'Build SPM Debug & Release'
+# - stage: Deploy
+#   dependsOn: Test
+#   condition: startsWith(variables['Build.SourceBranch'], 'refs/tags') # Deploy on tags only