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.
Just deleting all commented out lines. We can always restore from history.