v0.21.1

Fixed

• A column of single values is a list again. Its first line was taken
  for a caption over the rest, line after line, so every value became a
  heading, and a column of a few thousand values, a list of keywords,
  overflowed the stack and stopped the sync. A caption is now a line on its
  own above a table, or above a single note.
• One spreadsheet no longer stops a sync. Whatever stops a
  spreadsheet's conversion holds back that spreadsheet (ADR-026), with the
  kind of error as its detail, and the rest of the site is published.
• An unexpected sync failure names the kind of error, such as
  RangeError, and still never its message.