Feature: Add or delete a latent style

In order to determine which latent styles are defined in a document

As a developer using python-docx

I need a way to add and delete a latent style

Scenario: Add a latent style

Given a document having known styles

When I add a latent style named 'Foobar'

Then the document has one additional latent style

And latent_styles['Foobar'] is a latent style

Scenario: Delete a latent style

Given a document having known styles

When I delete a latent style

Then the document has one fewer latent styles

And the deleted latent style is not in the latent styles collection