Release Interrupt 9.0.0-alpha.1.
Release Interrupt 9.0.0-alpha.1.

 * Caret pin Extant to `1.0.15`. Closes #76.
 * Add badges to `README.md`. Closes #75.
 * Tidy `.travis.yml`. Closes #74.
 * Install `prove` at GitHub Actions. Closes #73.
 * Tidy `.gitignore`.
 * Use Proof file suffix. Closes #72.
 * Revert tests to Proof. Closes #72.
 * Skip 1 minutes Codecov action build. See #70.

Closes #77.

bigeasy/interrupt