Remove gemspec and Appraisals, update Gemfile for GitHub Pages

Deleted the custom gemspec and Appraisals files, and simplified the Gemfile to use the github-pages gem for plugin management. This streamlines dependency management and aligns the project with GitHub Pages' recommended setup.

Author: mazino2d

Appraisals

@@ -2,14 +2,6 @@
 
 source "https://rubygems.org"
 
-# 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
+gem "github-pages", group: :jekyll_plugins
 
-# Performance-booster for watching directories on Windows
-gem "wdm", "~> 0.1", :platforms => [:mingw, :x64_mingw, :mswin]
-  
 gemspec