Rework CI to add multi-version build and Maven repository caching

.github/workflows/ci.yml

@@ -0,0 +1,34 @@
+name: Java CI with Maven
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+  workflow_dispatch:
+
+jobs:
+  build:
+    name: Java ${{ matrix.java }}
+    strategy:
+      fail-fast: false
+      matrix:
+        java: [ 8, 11, 16, 17-ea, 18-ea ]
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Setup Java
+      uses: actions/setup-java@v2
+      with:
+        distribution: 'zulu'
+        java-version: ${{ matrix.java }}
+    - name: Cache local Maven repository
+      uses: actions/cache@v2
+      with:
+        path: ~/.m2/repository
+        key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
+        restore-keys: |
+          ${{ runner.os }}-maven-
+    - name: Build with Maven
+      run: mvn -B package