Maintenance release v1.3.0 — modernize project tooling

Replace custom Indexer system with standard gemspec, Travis CI with
GitHub Actions, and update Rakefile. Fix typo in version.rb module name.
Switch tests to minitest. Update URLs to HTTPS, clean up obsolete files.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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

@@ -1,8 +1,7 @@
-.reap/digest
 .yardoc
 doc
 log
 pkg
-web
-DEMO.md
-*.lock
+tmp
+Gemfile.lock
+*.gem