Migrate from Travis CI to GitHub Actions (#158)

While there, drop the now-obsolete Takari Maven plugin.

.github/workflows/build.yaml

@@ -0,0 +1,37 @@
+name: Build and verify
+on:
+  pull_request:
+  push:
+    branches:
+      - 'master'
+jobs:
+  build:
+    runs-on: ubuntu-22.04
+    strategy:
+      matrix:
+        jdk: [ 11.0.16, 17.0.4 ]
+    steps:
+        # We run the build twice for each supported JDK: once against the
+        # original Error Prone release, using only Error Prone checks available
+        # on Maven Central, and once against the Picnic Error Prone fork,
+        # additionally enabling all checks defined in this project and any
+        # Error Prone checks available only from other artifact repositories.
+      - name: Check out code
+        uses: actions/checkout@v3.0.2
+      - name: Set up JDK
+        uses: actions/setup-java@v3.4.1
+        with:
+          java-version: ${{ matrix.jdk }}
+          distribution: temurin
+          cache: maven
+      - name: Display build environment details
+        run: mvn --version
+      - name: Build project against vanilla Error Prone
+        run: mvn -T1C install
+      - name: Build project with self-check against Error Prone fork
+        run: mvn -T1C clean verify -Perror-prone-fork -Pnon-maven-central -Pself-check -s settings.xml
+      - name: Remove installed project artifacts
+        run: mvn build-helper:remove-project-artifact
+
+# XXX: Enable Codecov once we "go public".
+# XXX: Enable SonarCloud once we "go public".