Migrate to GitHub actions from Travis.

.github/workflows/ci.yml

@@ -0,0 +1,29 @@
+name: CI
+
+on:
+  push:
+    branches:
+      - dev
+      - master
+  pull_request:
+
+jobs:
+  build-and-test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: set up JDK 1.8
+        uses: actions/setup-java@v1.4.3
+        with:
+          java-version: 1.8
+
+      - name: Cache Gradle dependencies
+        uses: actions/cache@v2
+        with:
+          path: ~/.gradle/caches
+          key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle') }}
+          restore-keys: ${{ runner.os }}-gradle
+
+      - name: Build and run Tests
+        run: ./gradlew check --stacktrace

.github/workflows/docs.yml

@@ -0,0 +1,33 @@
+name: Build and deploy JavaDocs
+
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  build-and-deploy-docs:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: set up JDK 1.8
+        uses: actions/setup-java@v1.4.3
+        with:
+          java-version: 1.8
+
+      - name: Cache Gradle dependencies
+        uses: actions/cache@v2
+        with:
+          path: ~/.gradle/caches
+          key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle') }}
+          restore-keys: ${{ runner.os }}-gradle
+
+      - name: Build JavaDocs
+        run: ./gradlew aggregatedJavadocs
+
+      - name: Deploy JavaDocs
+        uses: peaceiris/actions-gh-pages@v3
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: ./build/docs