v0.17.0

Added

• A field can be derived from the folder a record sits in. A type declares from: sub-path on a field, and kac
  reads its value from the folders between the type's own folder and the file. policies/security/accs-access-by-identity.md
  carries category: security without a line of frontmatter saying so, and standards/platform/node/testing.md carries
  platform/node. A record saved straight into its type folder gets an empty value, so you start using categories by
  making a folder. The value reaches the generated index, its sort, and kac export.
• derived-key reports a derived field written by hand. The key is declared, so unknown-key admits it and cannot
  say that the value comes from the path. Delete the line, and file the record in the folder you want it to name.
• schema-shape reports a type whose folder: is not the name of the file declaring it. A document's type is
  read from the folder it sits in, and that lookup uses the schema file's name, so the two disagreeing left every
  record of the type unread while generate wrote into the folder nobody was reading. The two names now have to
  agree.

Changed

• A standard's axis field is gone, and category replaces it. Nothing read axis but one index column, which
  repeated the folder already shown in each row's link. The composition model stays: the rule-set binding a piece of
  work is the union of the folders that apply to it. Delete axis: from every standard.
• A policy's category is read from its folder rather than from its frontmatter. It is no longer a required enum
  of security, delivery, operations and governance. Move each policy into the folder its category named, delete
  the category: line, and the exported value is unchanged. The set of folders is now the corpus's own.

Fixed

• kac validate judges a #fragment against the headings alone. It read a record's frontmatter block as a
  heading, so fragment-resolves accepted a link naming an anchor no renderer offers. A link into a record is now
  held to the headings that record carries.