Isochronous v4.0.0-alpha.1

• Actually pass status into user function. Closes #40.
• Add GitHub Actions, Codecov and license badges. Closes #39. Closes #38. Closes #37.
• Convert to Markdown so as to add badges. See #39. See #38. See #37.
• Build with Actions, ship coverage to Codecov. Closes #36. Closes #35.

Closes #41.