Directory-based notes should repeat the directory name

Blarg allows notes to be either a single file, or a directory of related files with one primary. To create a directory-based note, the base name of the directory and the primary note file should be the same. For example,

note-title/note-title.md
Soft air/Soft air.md

This recommendation is based on the behavior of iA Writer and Obsidian. Using the naming convention above, iA Writer will default to inserting wiki links like [[note-title]] and Obsidian will default to [[note-title/note-title]]; both programs correctly resolve either link.

The alternative naming that Blarg was based on was to use index.md as the name of the primary note file, and special-case this in the code for compiling to HTML. With this convention, iA Writer and Obsidian both want to insert wiki links like [[note-title/index]], and both resolve to the correct file. Shortening the wiki link to [[note-title]] prevents them from resolving; instead they create a new note that’s a peer of the directory. The wiki links are forced to be a bit uglier.