go-tour: give each slide a unique name
go-tour: give each slide a unique name

This will allow us to use human-readable fragments when linking to
pages (eg, #methods instead of #37), make it easier to re-order slides,
and store the code samples in separate go files.

R=golang-dev, campoy
CC=golang-dev
https://codereview.appspot.com/6867048

BenjaminTsai/go-tour-zh-tw,BenjaminTsai/go-tour-zh-tw