Migrate from Travis CI to GitHub actions

.github/workflows/ci.yml

@@ -0,0 +1,91 @@
+name: CI
+
+on:
+  - push
+  - pull_request
+
+jobs:
+  format:
+    name: Format and compile with warnings as errors
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+
+      - name: Install OTP and Elixir
+        uses: actions/setup-elixir@v1
+        with:
+          otp-version: "23.0"
+          elixir-version: "1.11.2"
+
+      - name: Install dependencies
+        run: mix deps.get
+
+      # TODO: Enable in next release
+      #
+      # At the moment, we still have pending PRs etc.
+      # and introducing auto-formatting now would cause
+      # a ton of conflicts.
+      #
+      # - name: Check mix format
+      #   run: mix format --check-formatted
+
+      - name: Compile with warnings as errors
+        run: mix compile --warnings-as-errors
+
+  analysis:
+    name: Run static code analysis
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+
+      - name: Install OTP and Elixir
+        uses: actions/setup-elixir@v1
+        with:
+          otp-version: "23.0"
+          elixir-version: "1.11.2"
+
+      - name: Install dependencies
+        run: mix deps.get
+
+      - name: Analyze code
+        run: mix credo --strict
+
+  test:
+    name: Test Elixir ${{ matrix.elixir }}, OTP ${{ matrix.erlang }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - erlang: "23.0"
+            elixir: "1.11.2"
+          - erlang: "23.0"
+            elixir: "1.10.3"
+          - erlang: "22.3"
+            elixir: "1.9.4"
+          - erlang: "21.3"
+            elixir: "1.8.2"
+          - erlang: "20.3.1"
+            elixir: "1.7.4"
+          - erlang: "19.3"
+            elixir: "1.6.6"
+          - erlang: "18.3"
+            elixir: "1.5.3"
+
+    steps:
+      - uses: actions/checkout@v1
+
+      - name: Install OTP and Elixir
+        uses: actions/setup-elixir@v1
+        with:
+          otp-version: ${{ matrix.erlang }}
+          elixir-version: ${{ matrix.elixir }}
+
+      - name: Install dependencies
+        run: mix deps.get --only test
+
+      - name: Run unit tests
+        run: mix test --trace --exclude functional
+
+      - name: Run functional tests
+        run: mix test --trace --only functional