go.tools/godoc/blog: add PlayEnabled and GodocURL options
go.tools/godoc/blog: add PlayEnabled and GodocURL options

Also make NewServer take a Config, not *Config.

R=golang-dev, dsymonds
CC=golang-dev
https://codereview.appspot.com/13755044

webfd/go-zh.tools,bryanxu/go-zh.tools,bryanxu/go-zh.tools,8limbs/gotools,webfd/go-zh.tools,skyportsystems/go.tools,d0f/go-zh.tools,8limbs/gotools,skyportsystems/go.tools,d0f/go-zh.tools,skyportsystems/go.tools,d0f/go-zh.tools,d0f/go-zh.tools,bryanxu/go-zh.tools,skyportsystems/go.tools,8limbs/gotools,skyportsystems/go.tools,d0f/go-zh.tools,webfd/go-zh.tools,bryanxu/go-zh.tools,webfd/go-zh.tools,bryanxu/go-zh.tools,webfd/go-zh.tools