* ext/psych/lib/psych/visitors/yaml_tree.rb: support dumping Encoding
  objects.

* ext/psych/lib/psych/visitors/to_ruby.rb: support loading Encoding
  objects.

* test/psych/test_encoding.rb: add test

* ext/psych/lib/psych.rb: add version

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45221 b2dd03c8-39d4-4d8f-98ff-823fe69b080e