request: complete idempotent methods
see rfc2616: http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.

Intact idempotent HTTP methods should be:
GET, HEAD, PUT, DELETE, OPTIONS and TRACE
Merge pull request #274 from yorkie/complete-idempotent-methods

request: complete idempotent methods