Convert site to Jekyll

- Add Jekyll configuration (_config.yml)
- Create default layout with proper HTML structure
- Extract CSS to separate file (assets/css/main.css)
- Convert index.html to Jekyll format (index.md)
- Move image to assets directory
- Add Gemfile for Jekyll dependencies
- Backup original index.html

The site now uses Jekyll static site generator while maintaining
the same visual appearance and functionality as the original.

Gemfile

@@ -0,0 +1,25 @@
+source "https://rubygems.org"
+
+gem "jekyll", "~> 4.4"
+gem "minima", "~> 2.5"
+
+group :jekyll_plugins do
+  gem "jekyll-feed", "~> 0.12"
+  gem "jekyll-sitemap"
+  gem "jekyll-seo-tag"
+end
+
+# Windows and JRuby does not include zoneinfo files, so bundle the tzinfo-data gem
+# and associated library.
+platforms :mingw, :x64_mingw, :mswin, :jruby do
+  gem "tzinfo", ">= 1", "< 3"
+  gem "tzinfo-data"
+end
+
+# Performance-booster for watching directories on Windows
+gem "wdm", "~> 0.1.1", :platforms => [:mingw, :x64_mingw, :mswin]
+
+# Lock `http_parser.rb` gem to `v0.6.x` on JRuby builds since newer versions of the gem
+# do not have a Java counterpart.
+gem "http_parser.rb", "~> 0.6.0", :platforms => [:jruby]
+