Make things a bit more OO

[benbalter]

This pull request started out as an attempt to add a Repository class, that could accept a repository name and retrieve the repository's CNAME, but expanded to abstract much of the check logic out of a single giant class, into more object-oriented classes. Specifically:

• Move domain-specific checks to the Domain class
• Add new repo-level checks to a Repository class
• Create a new Site class to encompass Domain and Repository checks
• Abstract check!, valid? and reason logic to a Checkable class
• Create an Errors class to autoload all errors
• Make GitHubPages and HealthCheck modules, not classes

Still to do:

• Tests

[parkr]

You'd vendor a .env inside of lib/?

[parkr]

It might be good to defensively check the input here:

raise ArgumentError, "Expected string, got #{host.class}" unless host.is_a? String

I see a lot of undefined method for NilClass:nil in our future without it :)

[parkr]

For consistency with the rest of the class, this should either be Errors::InvalidRepositoryError, or all the others should have GitHubPages::HealthCheck:: 😄

[benbalter]

@parkr believe this should be ready for one more 👀, when you're ready. I believe I implemented everything you mentioned, plus tests, and simplified the to_hash logic by moving the methods that should become part of the hash logic to checkable.

[parkr]

Does this return the class or raise an error?

[benbalter]

Raises. What's the best way to note that?

[parkr]

Can we also ship #37?

[benbalter]

Can we also ship #37?

Looks like the conflict should be minimal. Once this merges, I can work on reconcile #37 and we can release a new version.