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.
Merge pull request #1482 from Ichimonji10/entity-path

(API) Make Entity.path overrides more consistent