add method for ProxyHttpServer object

[ttmars]

I will execute Proxy.OnResponse().DoFunc many times.

type ProxyHttpServer struct { respHandlers []RespHandler }

so，I hope clear respHandlers chain please add method for ProxyHttpServer to clear respHandlers

add method like this: func (proxy *ProxyHttpServer) ClearRespHandlers() { proxy.respHandlers = proxy.respHandlers[0:0] }

thank you