Maintenance release v2.2.0 — modernize project tooling

Replace custom Indexer system with standard gemspec, Travis CI with
GitHub Actions, and add Rakefile. Switch tests to minitest. Update
URLs to HTTPS, clean up obsolete files and .gitignore.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Author: trans

.gemspec

@@ -0,0 +1,21 @@
+name: Test
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        ruby: ['3.1', '3.2', '3.3', '3.4']
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby }}
+          bundler-cache: true
+      - run: bundle exec rake test

.github/workflows/test.yml

@@ -1,10 +1,7 @@
-.ergo/digest
 .yardoc
-doc/
-log/
-pkg/
-tmp/
-web/
+doc
+log
+pkg
+tmp
+Gemfile.lock
 *.gem
-*.lock
-