Crossbar

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* new: support forwarding of options.extra to native workers
* fix: error in wamp.session.list and wamp.session.count (1721)
* fix: ticket 1725 log on disconnect; don't bother checking before close (1726)
* fix: close not propagated properly from backend (for websocket and rawsocket) (1723)
* fix: handle disconnected transport during stop notification (1716)
* new: Support Fallback Resource from packages (1711)

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* new: allow running reverse web proxy service on root path ("/")
* new: set reverse web proxy HTTP forwarding headers
* new: extend WAP web service: allow loading Jinja templates from Python package,
check service configuration, allow running service on root path
* new: first-cut dealer timeout/cancel implementation (1694)
* new: expand reverse WAMP proxy worker docs
* fix: depend on autobahn (and xbr) v20.2.1 and refreeze all deps
* fix: improve logging for router transport starts
* fix: remove python 2 compatibility code / remove unicode strings (1693)
* fix: ticket 1567 mocks (1692)
* fix: use cpy3.7 docker base images (1690)

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* fix: use time_ns/perf_counter_ns shims from txaio and remove duplicate code here
* fix: CPython 3.8 on Windows (1682)
* new: comprehensive node configuration example / doc page

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* new: OSS proxy workers refactor (1671)
* fix: handle websocket vs rawsocket proxy clients (1663)
* fix: use python3.8 from ubuntu archives (1659)
* fix: snap ensurepip failure (1658)
* new: configurable stats tracking (1665)
* new: WAMP session statistics via WAMP meta API events (``wamp.session.on_stats``)

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* new: authrole configuration for WAP web services
* new: revise/improve WAMP proxy workers
* new: snap improvements + use py3.8
* fix: add Web-Archive service docs
* fix: remove legacy python 2 imports

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* new: router-to-router links (aka "rlinks", aka "r2r links") - enables WAMP router clustering and HA
* new: WAMP proxy workers - enables WAMP clustering and HA
* new: WAP-webservice (WAP = WAMP Application Page)
* new: Archive-webservice