Push arbitrary Go types on Lua stack

[aybabtme]

Should be able to push arbitrary types on Lua, such as structs with fields and methods. For instances:

func (l *lua.State) int {
    u, err := url.Parse(...)
    if err != nil { ... }
    return lua.DeepPush(l, u)
}

Would expose all the fields and methods of var u url.URL. Changing the fields from lua would change the fields in the actual u on the Go side, so that u.String() would reflect the changes made in lua:

u = url.parse("http://bing.com/search?q=dotnet")
u.scheme = "https"
u.host = "google.com"
q = url.query()
q.set("q", "golang")
url.rawQuery = q.encode()
equals("can change string", "https://google.com/search?q=golang", u.string())