(API) Make Entity.path overrides more consistent

The base `Entity` class provides a `path` method, and numerous subclasses extend
this method. Make those overrides more consistent:

* Provide the `which` variable as an argument when `super` is called.
* Use definition lists in docstrings.
not trying to nitpick, but this is the only section that still contains the ":id" notation instead of <id>. not a big deal at all, though.