[gemspec] Tweaked non-essential stuff

* dependency order
* double and single quotes
[gitignore] .bundle/
[rebuilding-with-rake] Introduce SlidesBuilder

This is an entry point to building out a presentation with rake.

In Rake parlance, ultimately, it might look something like:

create_presentation
  => [copy_reveal_js, copy_user_files,
      output_dir/slides.html,
      output_dir/index.html]

..But right now the only thing that's working is copy_reveal_js.
[rebuilding-with-rake] Whitespace Change

In the previous commit, I had to wrap the contents bin/reveal-ck in a
class. Both GLI and Rake use the 'desc' command and wrapping in a class
was done to side-step the issue.

See: https://github.com/davetron5000/gli/issues/153
[format] Re-wrapped the slides file in single quotes
[rebuilding-with-rake] Introduced copy_user_slides

Works in a similar fashion as copy_reveal_js, but this one copies user
content into the presentation.
[rebuilding-with-rake] Introduced create_slides_html

This reads in a slides file, ala slides.md, and translates it into HTML
which ends up being stored at slides/slides.html.
[rebuilding-with-rake] Introduced create_index_html

All features are passing again with one exception.
[rebuilding-with-rake] Config's merge_file is now merge

It's no longer file based.
[rebuilding-with-rake] Inverted Config behavior

Previously, if a value was set, it would not overwrite.

Now, if the last value set wins, so long as it's not a default value.
[rebuilding-with-rake] Started using the new Config

Back to 100% green again!
[rebuilding-with-rake] Added features that cover new directories that are copied
[rebuilding-with-rake] Rubocopped majority of project
[rebuilding-with-rake] Rubocop now permits trivial accessors in DSL
[rebuilding-with-rake] Extracted a method from merge
[rebuilding-with-rake] Split larger method into smaller ones
[rebuilding-with-rake] Standardized on 'setup'
[rebuilding-with-rake] Introduced RakeAware. Starting using throughout.
[copyright]
[rebuilding-with-rake] Deleted PackagedSlides

It's no longer needed now that we're using Rake in this fashion.