Support per-module checks

[RBusarow]

In grotesquely large codebases with thousands of modules, the initial check can take enough time that it's no longer trivial to just execute against all modules. If a developer is modifying the dependencies in a single module -- probably somewhere in a middle layer of the dependency graph -- they should be able to execute against that single module.

[tasomaniac]

For some rules, just starting from that module works. But some others, it may be required to go up until the root and cover ancestors.