Multipage collections in jekyll-theme-ed2

[karlstolley]

Rather than follow in the footsteps of ed v1, I want to handle collections so that longer works (e.g., The Narrative Life of Frederick Douglas) are:

• Broken up by major section (chapter, act, canto, etc.) into separate URLs for lighter-weight downloads and easier referencing by URL
• Provided a table of contents not from error-prone front matter, but by a collection of files that make up the longer work in the collections directory

Note that since Jekyll 3.7.0, collections can be organized by subdirectory: https://jekyllrb.com/docs/collections/ which means a work could be organized, for example,

└── _texts/
    └── a_famous_book/
        ├── chapter-01.md
        ├── chapter-02.md
        ├── chapter-03.md
        ├── chapter-04.md
        └── chapter-05.md

I will look into the proper baseline configuration to handle that in _config.yml, and also working through the collections in templates to generate tables of contents, etc.