Enable replacing feature and other config objects from the site scope to other objects

[briandominick]

Right now, most features and other theme settings draw from the site scope defined by Jekyll configuration files.

It would be nice to provide (at the point of expression in layout/include templates) an alternate source for any object. The object would need the same required properties, but this would enable proviing configuration in data files.

WORKAROUND: For now, the optimal means of achieving this is to source the different site-scoped objects in separate files and list all files in your Jekyll command using bundle exec jekyll build --config file1.yml,file2.yml. To break up the giant site.features scope into multiple files, you''ll need to compile multiple child objects into one, which is not handled by AsciiDocsy alone.