Setup GitHub Actions CI for automatic builds.

.github/workflows/activation.yml

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+name: Acquire activation file
+
+on:
+  workflow_dispatch: {}
+
+jobs:
+  activation:
+    name: Request manual activation file 🔑
+    runs-on: ubuntu-latest
+    steps:
+      # Request manual activation file
+      - name: Request manual activation file
+        id: getManualLicenseFile
+        uses: game-ci/unity-request-activation-file@v2
+        
+      # Upload artifact (Unity_v20XX.X.XXXX.alf)
+      - name: Expose as artifact
+        uses: actions/upload-artifact@v2
+        with:
+          name: ${{ steps.getManualLicenseFile.outputs.filePath }}
+          path: ${{ steps.getManualLicenseFile.outputs.filePath }}

.github/workflows/main.yml

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+name: Build my project ✨
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    name: Build for ${{ matrix.targetPlatform }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        targetPlatform:
+          - StandaloneWindows64
+          - StandaloneWindows
+          - StandaloneLinux64
+          - StandaloneOSX
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+        # with:
+        #   lfs: true
+
+      # Cache resued Library files to speed up compilation
+      - uses: actions/cache@v2
+        with:
+          path: Library
+          key: Library-${{ hashFiles('Assets/**', 'Packages/**', 'ProjectSettings/**') }}
+          restore-keys: |
+            Library-
+
+      # Test (No tests yet, leaving this here for future.)
+      # - name: Run tests
+      #   uses: game-ci/unity-test-runner@v2
+      #   env:
+      #     UNITY_LICENSE: ${{ secrets.UNITY_LICENSE }}
+      #   with:
+      #     githubToken: ${{ secrets.GITHUB_TOKEN }}
+
+      # Build project with Unity
+      - name: Build project
+        uses: game-ci/unity-builder@v2
+        env:
+          UNITY_LICENSE: ${{ secrets.UNITY_LICENSE }}
+          UNITY_EMAIL: ${{ secrets.UNITY_EMAIL }}
+          UNITY_PASSWORD: ${{ secrets.UNITY_PASSWORD }}
+        with:
+          unityVersion: auto
+          buildName: Heaven Studio
+          buildsPath: build
+          targetPlatform: ${{ matrix.targetPlatform }}
+
+      # Output
+      - uses: actions/upload-artifact@v2
+        with:
+          name: ${{ matrix.targetPlatform }}-build
+          path: ./build/${{ matrix.targetPlatform }}/