Rename modules for consistency

[svlandeg]

Description

The entity_ruler and attribute_ruler components remain unchanged in their naming, but this PR updates their Python modules to the same, consistent name. In v4, this will break imports from the old entityruler.py and attributeruler.py that need to be rewritten to import from entity_ruler.py and attribute_ruler.py instead.

This change makes the code base more consistent with entity_linker, span_ruler etc, and makes the naming of the Python modules consistent with the camel casing of the class names.

Types of change

Python module refactoring

Checklist

• I confirm that I have the right to submit this contribution under the project's MIT license.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.

[adrianeboyd]

This is pleasingly minimal.