Fix status code in documents [ci skip]

RFC 6585 Additional HTTP Status Codes
http://www.ietf.org/rfc/rfc6585.txt
Added missing closing bracket for markdown url in guides [ci skip]
Merge pull request #11701 from morgoth/link-fix-in-guides

Added missing closing bracket for markdown url in guides [ci skip]
Merge pull request #11699 from satococoa/fix-render-status-symbols-document

Fix status codes in document
Fix `current_page?` when the URL contains escaped characters

In some cases webservers like nginx send the escaped characters
lowercased to the Rails application. The current_page? helper was
comparing the escaped strings that are different since Ruby escapes the
URL using uppercased characters.