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

Author: scordio

.github/workflows/ci.yml

@@ -0,0 +1,23 @@
+name: Java CI with Maven
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    name: Java ${{ matrix.java }}
+    strategy:
+      fail-fast: false
+      matrix:
+        java: [ 8, 11, 17, 18-ea, 19-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 }}
+        cache: maven
+    - name: Build with Maven
+      run: mvn -B package