Support middleman v5

[le0pard]

No description provided.

[le0pard]

Should also close #21

[tdreyno]

This is really great, thank you.

I am curious, what is the goal of using an options hash over the old option approach for the compress items? If possible, I'd love to avoid breaking API compatibility with v4 config files.

[le0pard]

@tdreyno thanks for feedback.

I moved its to separate config key, because thinking not to mix with additional options, like already added ignore and content_types (and maybe some future general options).

I can back all configuration on one level, it is not an issue (maybe just need little more logic to remove general settings from config before pass its to HtmlCompressor).

Just confirm, that this looks good for configuration to move all on one level :)

[tdreyno]

Confirmed. Lets go back to one level so this doesn't break existing configs. Then 👍

[le0pard]

Done. Please check @tdreyno