v0.42.0 — What a composition can express

Since v0.41.0, anyone can write a composed rune. This milestone widens what a definition can say. Templates may be indented, and refrakt format indents nested runes for you. Content may be split on --- into named zones, a sections model may treat content with no headings as one section, and each can walk the items of a plain list. An itemModel declared in YAML now extracts its fields instead of leaving every one empty (SPEC-169, SPEC-170).