Dynamic environment updates

Parse `.env.example` (in a simple fashion) and create `.env` based on the merge of the default values and any user-specified ones.

You also [previously asked about disabling provisioning](https://github.com/alias1/huginn-chef/pull/1#discussion_r17517264). Vagrant supports disabling provisioning via the `--no-provision` command line flag (opt-out behavior) which I find more convenient. We could switch to an opt-in behavior, but I think provisioning by default is the expected behavior. Either way, we should document the additional behavior in the README.
Do we want to let the huginn user run anything with sudo, or only the stop/start/restart type commands.

I'm somewhat inclined to keep it to the bare minimum required personally.

* Service management: Stop, Start, Restart, Status (`stop huginn`, `start huginn`, `status huginn`, `restart huginn`?)
* Foreman export (`sudo -E bundle exec foreman export...`)