Pyramid-blacksmith

------------------------------
* Release an alpha middleware for zipkin based on zk
Stay undocumented until it has been tested on prod
* Update deps

------------------------------
* Add a middleware to inject a header statically from the conf

------------------------------
* Fix the error_parser implementation1

------------------------------
* Update to blacksmith 2.0

------------------------------
* Broken release :/

------------------------------
* Readd previews dependency prometheus_client, always required
* Improve developper experience while writing tests due to prometheus_client
* Update the documentation