和 ENV 有关的方法：
auth_type
gateway_interface
path_translated
remote_host
remote_ident
remote_user
remote_addr
server_name
server_protocol
accept
accept_charset
accept_encoding
accept_language
cache_control
from
negotiate
pragma
其它：
abort
await_commit
await_sent
body
body=
body_parts
close
code
commit!
committed?
content_type=
cookies
delete_cookie
location & redirect_url
location=
message & status_message
response_code
sending!
sending?
sent!
sent?
set_cookie
status=
to_a & prepare!
to_ary