Feature: Add a run with optional text and style

In order to add distinctively formatted text to a paragraph

As a python-docx programmer

I want a way to add a styled run of text in a single step

Scenario: Add a run specifying its text

Given a paragraph

When I add a run specifying its text

Then the run contains the text I specified

Scenario: Add a run specifying its style

Given a paragraph

When I add a run specifying the character style Emphasis

Then run.style is styles['Emphasis']