Add functions for capturing output and basic file manipulation

[mjambon]

See the new tests in Test.ml for sample usage.

Closes #57

PR checklist:

• [x] Purpose of the code is evident to future readers
• [x] Tests are included or a PR comment includes a reproducible test plan
• [x] Documentation is up-to-date
• [ ] A changelog entry was added to CHANGES.md for any user-facing change

Check out CONTRIBUTING.md for more details.

[aryx]

thx