Improve repository.

- add kokuwa checkstyle
- add dependabot
- add dependency documentation
- add code owners
- add codeql
- add license badge

.github/workflows/pullrequest.yaml

@@ -0,0 +1,26 @@
+name: PullRequest
+
+"on": pull_request
+
+jobs:
+
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2.4.0
+      - uses: actions/setup-java@v3.0.0
+        with:
+          distribution: temurin
+          java-version: 11
+          cache: maven
+      - run: mvn -B dependency:go-offline
+      - run: mvn -B verify
+      - uses: dorny/test-reporter@v1.5.0
+        if: failure()
+        with:
+          name: surefire
+          path: '**/target/surefire-reports/*.xml,**/target/invoker-reports/*.xml'
+          reporter: java-junit
+          list-suites: failed
+          list-tests: failed
+          fail-on-error: false