Migrate to GitHub Actions for CI

.github/workflows/test.yml

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+name: Test
+
+on: [push, pull_request]
+
+jobs:
+  build:
+
+    name: Build and test
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        otp: ['22.3']
+        elixir: ['1.10.4']
+
+    services:
+      postgres:
+        image: postgres:12
+        ports: ['5432:5432']
+        env:
+          POSTGRES_USER: postgres
+          POSTGRES_PASSWORD: postgres
+        options: >-
+          --health-cmd pg_isready
+          --health-interval 10s
+          --health-timeout 5s
+          --health-retries 5
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Set up Elixir
+      uses: actions/setup-elixir@v1
+      with:
+        elixir-version: ${{matrix.elixir}}
+        otp-version: ${{matrix.otp}}
+
+    - name: Restore dependencies cache
+      uses: actions/cache@v2
+      with:
+        path: deps
+        key: ${{ runner.os }}-${{ matrix.otp }}-${{ matrix.elixir }}-mix-${{ hashFiles('**/mix.lock') }}
+        restore-keys: ${{ runner.os }}-mix-
+
+    - name: Install dependencies
+      run: mix deps.get
+
+    - name: Check formatting
+      run: mix format --check-formatted
+
+    - name: Setup EventStore test database
+      run: MIX_ENV=test mix do event_store.create, event_store.init
+
+    - name: Run tests
+      run: mix test

.tool-versions

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+elixir 1.10.4-otp-22