Add support for a local directory tree configuration file, a .batconfig

[bberberov]

Could you add support for a local directory tree configuration file to supplement the systemwide and user configuration files. Similar to how .gitattributes, or .editorconfig affect the configuration of their tools. One of the main uses would be for custom --map-syntax statements, which "travel" when the directories are moved, or repos are checked out. .batconfig seems like an appropriate name for this.