* siri/logger/std-recreate-file-if-rotated/OTP-15469:
  [logger] Re-create log file if deleted

* siri/logger/unexpected-exit-from-simple/ERL-788/OTP-15466:
  [logger] Unlink simple handler before terminating

This is an update to logger_std_h, which makes it play well with tools
like logrotate.

* maint-21:
  Updated OTP version
  Prepare release

This avoids an unexpected EXIT message with reason normal beeing
printed from logger_server when the simple handler is replaced. It
will still be printed if it exists unexpectedly.

* siri/logger/ets-read-concurrency/ERL-782/OTP-15453:
  [logger] Add read_concurrency to options for logger ets table

* siri/logger/refactor-built-in-handlers:
  [logger] Write asynchronously to disk log
  [logger] Add statistics counter for drops due to message bursts
  [logger] Further refactor built-in handlers
  [logger] Move common handler code to logger_h_common