Major refactoring

Usage now looks like this to be more symmetrical with forego/foreman:

```
hsup start -d docker -c 2 -a simple-brandur
hsup start -d docker -c 2 -a simple-brandur program
hsup run -d docker -c 2 -a simple-brandur hello world
```

(Note that the last example is buggy in that hsup does not notice that the Docker containers have exited and contines to run happily doing nothing. We need to get some supervision happening.)

Some changes/improvements:

* Executor type has now been changed to closely resemble a running dyno.
* Executors have names like `web.1` and `web.2`. Container names are derived from them.
* Parallelized executor stop and start.
* Supports encrypted Docker API connections by checking for `DOCKER_CERT_PATH`, which seems to be the preferred communication method these days.
* FactoryFactoryFactories have been removed ... for now.

Still needs many improvements unfortunately. `main.go` is still a disaster.

/cc @fdr