Added test for `deps-subtract` tech
Added test for `deps` tech
Added test for `files` tech
Fixed `toBemdecl` method of `Deps`
Fixed `fromBemdecl` method of `Deps`
Fixed `levels` tech
Fixed `bemdecl-merge` tech
Fixed `bemdecl-from-bemjson` tech
Used `build-flow` for `bemdecl-merge` tech
Used `build-flow` for `deps-merge` tech
Used `build-flow` for `deps-subtract` tech