Add 'config' command

[melriffe]

This command serves two purposes:

1. to generate a blank configuration file
2. to load a configuration file

Secondarily, and this might go in a separate ticket/milestone, add sub-commands to add/edit a config file.

I will need to document the order in which configuration items are processed.

[melriffe]

I'm going to change this ticket's goals. This will not be a new command. The app will be modified to create a new 'default' configuration file when one does not already exist.

I'm going to change TTY::Config to only look in the user's home directory. But... and this is the second change, I'm going to add a global option/flag/argument that allows a user to specify a different configuration file.

If I can't get TTY::Config to place nicely with those requirements I will kick it to the curb.

[melriffe]

I believe, though, the path forward is to make Hammerhead.configuration receive its configuration object rather than build one. This way, I can inject the configuration into the tool.

At least that's the goal.

[melriffe]

I just made Hammerhead::Configuration.config settable. And I think the reason I want something injectable is because I hope to be able to support command-line, ENV, and configuration file settings. I think I'll need a unified configuration object that is injected into Hammerhead::Configuration.

I'm vacillating between simple and complex - I might opt for simple and only go to complex when needed - which I don't need right now.

[piotrmurach]

The tty-config can read and write configuration in many formts including handling of env variables. It stores everything in a deeply nested hash. So, for example, you can read arbitrarily complex configuration options from users. Let's say you can config add command that takes the setting and value:

hammerhead config add a.b.c 1

Then you can invoke set on the tty-config instance:

config.set("a.b.c", value: "1")

Which will result in the following configuration hash:

 # => {a: {b: {c: "1"}}}