go-tour: move code snippets to article-specific directories

As the prog/tour directory grows it becomes more difficult to see
what belongs where. Also the prog/tour directory hierarchy is one
level too deep.

Here's the code used to make this change:

        for article in *.article; do
                base=$(echo $article | sed 's/.article//')
                mkdir $base
                gofiles=$(grep '^.play' $article | awk '{print $2}' | sed 's_prog/tour/__' | sort -u)
                for f in $gofiles; do
                        hg mv prog/tour/$f $base/$f
                done
                sed -i '' 's_prog/tour_'$base'_' $article
        done

        # catch dreg masked by "#appengine: " comment directive
        hg mv prog/tour/sandbox.go welcome/

LGTM=campoy
R=campoy
CC=golang-codereviews
https://golang.org/cl/111250043
78 files changed