What change does this introduce?

This PR adds the report.Report type and several associated types which represent a human-readable report about the activity within and final result of a test.

What issues does this relate to?

• Fixes Refactor report building so that it can be used outside of expectations. #162
• Prepares for Build a meaningful report when a handler panics with dogma.UnexpectedMessage. #118
• Prepares for Annotate the engine logs to indicate when expectations pass/fail. #161

Why make this change?

To allow for a consist report building and rendering experience regardless of whether the test result was determined by an Expectation or by some other occurrence.

Is there anything you are unsure about?

No