* lib/uri/mailto.rb: update to latest specs, RFC 6068 and HTML5.

* lib/uri/mailto.rb (HEADER_PATTERN): removed.

* lib/uri/mailto.rb (HEADER_REGEXP): use RFC 6068 hfields.

* lib/uri/mailto.rb (EMAIL_REGEXP): use HTML5 email regexp.

* lib/uri/mailto.rb (URI::MailTo.build): support multiple to addresses.

* lib/uri/mailto.rb (URI::MailTo#initialize): Support multiple to
  addresses. Don't check with regexp, only split.

* lib/uri/mailto.rb (URI::MailTo#check_to): verify by matching
  URI path-rootless and HTML5 email regexp with unescaped one.

* lib/uri/mailto.rb (URI::MailTo#check_headers): verify only by
  HEADER_REGEXP.

* lib/uri/mailto.rb (URI::MailTo#set_headers): don't check by
  HEADER_REGEXP, only split it.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46590 b2dd03c8-39d4-4d8f-98ff-823fe69b080e