Provide more organized output and sorting

[gjtorikian]

Closes #72.

Would appreciate some 👀 from @penibelst when you have the 🕥.

I could not figure out how to do neat ascii separators, so I went with * instead. I also apologize for the massive changes in how tests are written, it was a refactor that needed to happen.

[doktorbro]

What do you think about further refactoring?

class Proofer do

  def run 
    issues
    output
  end

  def issues 
    # return an array of issues
  end

  def output 
    # output the issues
  end

end

With this architecture we could test the issues and the output separately. Moreover users could override these methods.

[gjtorikian]

What do you think about further refactoring?

I like it, but I am super behind on releasing a new gem that addresses several bugfixes. I'll open an issue as a reminder for this.