stratify 1.0.1

Fixed

• Span fields no longer carry ANSI escape codes into files or colourless
  consoles. The escape codes were coming from span-field caching: the
  layer's own ANSI flag — which defaulted on — decides how a span's fields are
  rendered into the cache every event then prints verbatim, and the sinks only
  ever set the flag on the event format. Found live: a web service's
  per-request span (http_request{method=…}) arrived in its log file wrapped
  in italic/dim codes with colour configured off everywhere.

  The file sinks also get their own cache now (a distinct field-formatter
  type), so a coloured console beside a text file cannot bleed escape codes
  into it either — previously the two shared one cache and whichever layer
  formatted a span first decided what the other printed, which is why services
  had to switch console colour off to protect their files. Both regressions
  are pinned by tests that fail against the previous release.