first pass at adding heroku deploy/update tasks

Usage:

```shell
$ bundle exec rake deploy
$ bundle exec rake update[heroku-app]
```

I expect this still needs work, but wanted to have something more concrete to discuss. A few points:

* I wanted to put this stuff in a heroku rake namespace, which seemed cleaner. But since we require './app' it seems that rake namespace is getting over written by sinatra namespace, so it errors if I try to use it here.
* You mentioned reducing dependencies. A couple of these (netrc, rendevzous) would be hard to do without, so the dependencies will have to be different regardless I suspect. Which ones are exceptable vs which should be cut.
* I kind of wanted to put it in a separate file and just require from the main Rakefile, but wasn't sure where to put it.

@swanson Hopefully moving in the right direction, even if there is work lef to do. Would appreciate review/feedback. Thanks!