Vault

Hello Joseph,

I've gone ahead and added Hubcap::Vault that can be used to store sensitive data. 

By default, it saves the data to ```.vault.yaml``` and also reads from this location.

There is a new bin script that will generate an initial config by running ```hubcap-vault --bootstrap```

An example of the usage after creating a config file
```ruby
require(Path.join(Dir.pwd, ".vault.rb"))
vault = Hubcap::Vault.new(:prod)
vault.store(:key, "data")
vault.save

vault[:key]
```

I am not sure if you are comfortable including this with hubcap or if you prefer I pull this into it's own Gem.

--Dan