Automatically replace example output in Markdown

[zupo]

Current workflow:

1. Do some changes in my CLI program.
2. Run tesh to see what output changed where.
3. Manually fix the expected output in shell session examples.

Ideal workflow:

1. Do some changes in my CLI program.
2. Run tesh --replace replaces the expected output in shell session examples with actual output.
3. No need for manual copy/pasting changes. Use git diff to review if changes make sense.

[zupo]

No idea how to handle ... inline / multiline ignores.