# Functions
AcquireWriter 从池中获取 Writer.
NewContext 创建一个 Context 实例.
ReleaseWriter 将 writer 放入池中.
TrimHeaderValue 返回第一个 例如: Content-Type: text/html; charset=utf-8 返回: text/html.
WithCookieDomain domain: https://tools.ietf.org/html/rfc6265#section-4.1.2.3.
WithCookieHTTPOnly secure: https://tools.ietf.org/html/rfc6265#section-4.1.2.6.
WithCookieMaxAge .
WithCookiePath path: https://tools.ietf.org/html/rfc6265#section-4.1.2.4.
WithCookieSecure secure: https://tools.ietf.org/html/rfc6265#section-4.1.2.5.
WithCookieSign 对 cookie 进行签名.
WithCookieVerify 对有签名的 cookie 进行验证.