feat: migrate CI to Github Actions (#27)

Migrate CI from Azure Pipelines to GitHub Actions, point it to the main branch.

.github/workflows/CI.yml

@@ -0,0 +1,45 @@
+name: CI
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+  schedule:
+    - cron: "0 0 * * *"
+
+jobs:
+  powershell-core:
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
+    runs-on: ${{ matrix.os }}
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Restore
+        run: tools/restore.ps1
+        shell: pwsh
+
+      - name: test
+        run: tools/run-tests.ps1
+        shell: pwsh 
+
+  windows-powershell:
+    runs-on: windows-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Restore
+        run: tools/restore.ps1
+        shell: powershell
+
+      - name: test
+        run: tools/run-tests.ps1
+        shell: powershell 
+
+      - name: Test manifest
+        run: Test-ModuleManifest -Path ./FeatureFlags.psd1
+        shell: powershell

README.md

@@ -1,4 +1,3 @@
-[![Build Status](https://dev.azure.com/PowerShell-FeatureFlags/PowerShell-FeatureFlags/_apis/build/status/microsoft.PowerShell-FeatureFlags?branchName=master)](https://dev.azure.com/PowerShell-FeatureFlags/PowerShell-FeatureFlags/_build/latest?definitionId=1&branchName=master)
 [![Nuget](https://img.shields.io/nuget/v/FeatureFlags.PowerShell)](https://www.nuget.org/packages/FeatureFlags.PowerShell/1.0.0)
 [![Platforms](https://img.shields.io/powershellgallery/p/FeatureFlags.svg)](https://www.powershellgallery.com/packages/FeatureFlags/)
 [![FeatureFlags](https://img.shields.io/powershellgallery/v/FeatureFlags.svg)](https://www.powershellgallery.com/packages/FeatureFlags/)