v0.8.0

Added

• A corpus declares the shorthand another corpus cites it by. .corpus.yaml carries a top-level
  shortcode:, which is the eng in eng:pol-VURM.TIMEBOX. kac validate refuses a spelling a
  citation cannot carry, and one a type has already taken as its id prefix. kac export states the
  declared shortcode in its manifest, so a consumer holding several exports knows which one answers a
  scoped citation. kac new writes the key with no value: a shortcode cannot be changed once another
  corpus has cited it, so it is filled in when one is about to.

Fixed

• kac validate reads a record whose frontmatter carries a complex key. A key written as a sequence
  or a mapping is legal YAML and names no field. It was reported as frontmatter that would not parse,
  which named the wrong fault. It now arrives as an empty key, which unknown-key reports against the
  document that wrote it.