Release Avenue 0.2.0-alpha.1.
Release Avenue 0.2.0-alpha.1.

 * Create Markdown readme with badges. Closes #47.
 * Build with Actions, ship coverage to Codecov. Closes #46. Closes #45.
 * Tidy `.gitignore`. Closes #44.
 * Remove `/.proof.out` from `.gitignore`. Closes #43.
 * Convert test to Proof. Closes #42.

Closes #48.

bigeasy/avenue,bigeasy/avenue