Special dir-related fields are now start_dir, root_dir, leaf_dir, work_dir, and build_dir
Hancho files in a submodule can be loaded via load(root="submodule/path", file="build.hancho)
Each Hancho module now gets its own 'config' object extended from its parent module (or global_config). This prevents submodules from accidentally changing global fields that their parent modules use while still allowing sharing of configuration across files.