• Added support for bootstrapping WebSockets via HTTP/2, as described in
  RFC 8441.
• A new directive 'H2WebSockets on|off' has been added. The feature is
  disabled by default for compatibility reasons.
• In Apache httpd development trunk (e.g. version 2.5.x) it is possible to use
  this with the proxy module to reverse proxy to a backend WebSockets server.
  This requires some new internal plumbing code in the server for getting I/O
  events on the HTTP/2 stream serving the connection.
  This "plumbing" is planned to be ported back into Apache 2.4.58.
• For implementors of Apache modules using WebSockets, mod_h2 offers an
  optional function that provides an alternative to "older" Apache versions.
  See http2_get_pollfd_from_conn, declared in mod_http2.h.