Refactor build.rb

Refactored the `build.rb` file. A couple main changes:

* `snake_case` variables and methods to conform to the [github style guide](https://github.com/styleguide/ruby) (as well as overall Ruby conventions)

* Encapsulate the building of the blog in an object, and add component methods to add to the implicit documentation of the class. Then, call a single method on the class with a single responsibility: to build the blog. Better object-oriented style

In the README, you talk about some Ruby hackery to create the blog posts. What you're doing is actually really clever (and something I never would've thought of), so I think if we refactor it a bit (with this PR), you don't really have to call it hackery anymore. Maybe "Ruby cleverness".