Auto merge of #3004 - ehiggs:master, r=alexcrichton

Resubmission of templating PR (#1747)

This is a manual rebase of the older #1747 PR which was basically unrebasable due to the time it's been dormant.. This implements templating for Cargo and is basically the work of Greg Chapple (@gchp).

I'd love for this feature to move forward since it's really tedious to create all the directories (e.g. `src/bin`) and copy paste docopt examples which I then edit. Then implement the `main` program to delegate to the subcommands in `src/bin`, etc.