Maintenance release v1.6.0 — modernize project tooling

Replace custom Indexer system with standard gemspec, Travis CI with
GitHub Actions, and Assembly/detroit/ergo with Rakefile. Fix Fixnum
reference for Ruby 3+ compatibility. Simplify version.rb. Fix typos,
update URLs to HTTPS, move site from gh-pages to docs/, and clean up
obsolete files.

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

Author: trans

.github/workflows/test.yml

@@ -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 demo

.gitignore

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