go-tour: add solution for HTTP exercise
go-tour: add solution for HTTP exercise

Fixes issue 176.

LGTM=minux.ma
R=golang-codereviews, minux.ma, mikioh.mikioh
CC=golang-codereviews
https://codereview.appspot.com/96650043

minux/go-tour-zh,Go-zh/tour-old,minux/go-tour-zh,Go-zh/tour-old