Now all helpers can be overridden by custom implementations without editing JB source. Just define a helper's 'engine' as 'custom' in the _config.yml file and provide a helper file of the same name in _includes/custom/. This helps users cleanly upgrade JB versions since they no longer need to edit the files directly.
This is because 'setup' will need to be included in every post/page file if we want to have access to BASE_PATH. So I figure 'setup' will be a good access path for any future inclusions we need to make
