mod_h2 v1.15.21

• Making h2 connection "mood swings" to ignore clients resetting
  requests which have at least produced the response headers and
  one DATA chunk. This targets long-running requests like
  websockets and server-side-events (SSE), where a RST_STREAM
  ius the cleint's only option of terminating such requests.
  With this change, clients are no longer punished for it.
  See also: https://bz.apache.org/bugzilla/show_bug.cgi?id=65402
  (background: "mood swings" influence how many resources are
  available to a connection, e.g. how many h2 workers may be
  working for it at a given point in time.)
• Making H2Min/MaxWorkers behave as intended again. The module will initially
  create H2MinWorkers threads and add up to H2MaxWorkers when needed. These
  additional workers time out when idle after H2MaxWorkerIdleSeconds and
  disappear again.
• When the shutdown of a child is detected (e.g. graceful shutdown), the
  module will terminate all idle workers above H2MinWorkers right away.
  This detection currently only happens when a HTTP/2 connection is active.
  See also #212.
• Restoring compatibility with apache httpd 2.4.48 again.
• Adding a docker image for testing on archlinux. Use:

   > docker-compose build archlinux
   > docker-compose run archlinux

• Adding a docker image for testing on Debian 'sid'. Use:

   > docker-compose build debian-sid
   > docker-compose run debian-sid