Add remote file opening via HTTP

[brettchalupa]

This adds support for loading the markdown and JSON from remote servers
by using open-uri. This means the docs can live outside of the
application server and not need to be generated or checked into the app.

The usecase for doing this is so that a Continuous Integration (CI)
server can generate the docs since it is already setup for the test
environment, which RAD requires. Then, after generation, it uploads the
RAD docs (JSON and markdown files) to a static file host, like AWS S3,
and then those docs get served to the application environments when
viewing the API docs.

This lets the docs be viewed in live application environments without
checking the docs into the app since they may change often.

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Let me know if this change is fitting for Apitome; if not, no worries. If I
need to add specs or adjust the Ruby style, totally let me know.

Thanks for building such a great doc viewer. 😄

[jejacks0n]

I absolutely love the idea, but don't have the time to review it right now.. please give me a few days to get back to you on this. I've been meaning to give this project some needed love and attention, but work has been taking it's toll. =)

[brettchalupa]

@jejacks0n No rush or worries at all, thanks!

[jejacks0n]

I'll merge it and see how it plays out. =) thanks again.