Add pluggable - A library to build plug-like pipelines (#4855)

Co-authored-by: Simone Vittori <[email protected]>

README.md

@@ -797,6 +797,7 @@ There are [other sites with curated lists of elixir packages](#other-awesome-lis
 * [plug_session_memcached](https://github.com/gutschilla/plug-session-memcached) - A very simple memcached session store for Elixir's plug.
 * [plug_sigaws](https://github.com/handnot2/plug_sigaws) - AWS Signature V4 authentication protection for Phoenix/Plug Routes ([Docs](https://hexdocs.pm/plug_sigaws/PlugSigaws.html)).
 * [plug_statsd](https://github.com/jeffweiss/plug_statsd) - A plug for automatically sending timing and count metrics to statsd.
+* [pluggable](https://github.com/mruoss/pluggable) - Build `plug`-like pipelines with your own token (instead of `%Plug.Conn{}`).
 * [plugs](https://github.com/sugar-framework/plugs) - Collection of Plug middleware for web applications.
 * [plugsnag](https://github.com/jarednorman/plugsnag) - Bugsnag notifier for Elixir's plug.
 * [raygun](https://github.com/cobenian/raygun) - Capture bugs and send them to Raygun.