* Support XDG_CONFIG_HOME for gemrc.
* Support XDG_DATA_HOME for .gem
* Added test for XDG_DATA_HOME
* Do not reuse environmental variable.
* Unify .rdoc path to RDoc.home.
* Support XDG_DATA_HOME for .rdoc
* Ignore exists?
* Extracted config_home path
* Use XDG_CONFIG_HOME for default credential path
* Fixed inconsistency location.
* Fixed the broken tests.
* Support XDG_CONFIG_HOME for irbrc
* Introduce Gem.cache_home as XDG_CACHE_HOME
* Use Gem.cache_home instead of Gem.config_home for the credential file of RubyGems.
* Initialized the old configurations
* Fixed test failure related the configuration initialization
* restore XDG_DATA_HOME
* Fixed the broken examples of bundler with XDG_*
* Do not modify environmental variable on test file
* Use XDG_DATA_HOME insted of XDG_CACHE_HOME for credential file
* stub out Gem.data_home
* Move dir accessor to defaults.rb file
* Use XDG_DATA_HOME for signed gem features
* Use XDG_DATA_HOME for spec cache
* Do not rely on Gem.user_home
* Gem.user_home is always exists. Don't need to use FileUitls.mkdir_p
* Bump support version to RubyGems 3.2.0+
* Removed the needless fallback configuration
* Fixed the inconsistency methods that are find_config_file and config_file
* Use Gem.configuration.credentials_path instead of hard-coded path
* gem_path is always provided
* Removed the duplicated code of find_home
* Also removed the duplicated code of user_home
* use Gem::UNTAINT instead of untaint for surpressing the warnings
* Use File.directory
* Restore XDG_DATA_HOME
* Use File.write
