Release 3.12.1

Release 3.12.1

* [Feature] Add /bayes/classifiers HTTP endpoint
* [Feature] Further improvements in scheduling next checks
* [Fix] Another fix for maps concurrent load
* [Fix] Do not add log tag header in milter logic
* [Fix] Do not explicitly add Connection header if it's there
* [Fix] Fix proxy headers duplication
* [Fix] Fix several issues with the lua_logger
* [Fix] Make logger more graceful when dealing with format arguments
* [Fix] Try to avoid incomplete writes
* [Rework] Eliminate maps locking