0.10.0+dune

CHANGES:

• Replace references and mutable fields by atomic references to avoid
  race conditions (dbuenzli#56). Thanks to Nathan Taylor for reporting.
• Fix Logs.{err,warn}_count. The counts were counting the reports
  not the logs which is not what the spec says. This means the counts
  were wrong when the reporting level was below the corresponding
  level (dbuenzli#55). Thanks to Mathieu Barbin for the report.
• Fix Log.Tag.list always returning the empty list.
• Logs.format_reporter and Logs_fmt.reporter replace a few format
  strings and ^^ uses by direct calls to Format primitives.
• Requires OCaml >= 4.14.
• Use Format.pp_print_text instead of our own.
• Export logs from each sub library.