Add a more formal "guides" section for beginners (like Rails Guides)

[andrewhavens]

I feel like the current "share a tutorial" does not achieve the goal of guiding a beginner to write games in Ruby. We need a more formal, curated guides section (like http://guides.rubyonrails.org). Maybe the categorization feature will help with this.

[andrewhavens]

• Add ability to navigate to a "Guides" page (add a link to this page in the nav bar).
• Add ability to create a new "Category" (GuidesCategory model) on this page
• List all of these Categories on the Guides page
• Add ability to create a new "Guide" post
  • Use single table inheritance to create a subclass of Post called Guide. Some work has already been done on this (in Implement Stackoverflow API  #45) to create an ExternalPost class.
  • All of the behavior should be the same as Post, but it should have a default tag of guide
  • Add ability to add a guide post to a category within the create guide form.
• The guides page can look very similar to http://guides.rubyonrails.org (a list of categories and their guides)

An extra feature that would be nice to have (not required):

• Anyone can edit a guide, but when they save it, it goes to a guide_revisions table, which requires a site admin to approve before it can go live.
• The guides always reference the latest approved revision.

Am I missing anything? Let me know if you have any more questions about this.

[andrewhavens]

Most of this has been built with #60