Improve String#eql?

String#eql? is not alias of String#==.
Fix "Z" in pack-template
Standardize String case-converter links
Adjust String#downcase to other case-converter
Fix String#downcase{!} examples
Fix weird example of String#capitalize!
Fix typo on String#=~ exception
Update examples in rexml
Merge branch 'master' of github.com:rurema/doctree
Merge pull request #18 from kachick/printf-name

Add `reference by name` on printf-format [Bug#8618]
Remove garbage
Update printf-format
Merge pull request #4 from kachick/improve-string-eql_p

Improve String#eql?
Merge pull request #5 from kachick/fix-pack_template_Z

Fix "Z" in pack-template
Merge pull request #42 from kachick/string-case-converter

Fix String case-converter
Merge pull request #43 from kachick/string-match

Fix typo on String#=~ exception
Merge pull request #44 from kachick/string-ord-exception

Fix String#ord exception class
Fix syntax error
Update method_missing exception class

* [1.6](https://github.com/ruby/ruby/blob/e247c4e598dd7807c24173a6c4b92a8dfe0b1caf/eval.c#L4175)
* [1.8.5](https://github.com/ruby/ruby/blob/82ea308dcf767a779c7b3efd930f8d13ea50a5aa/eval.c#L5566)