chore: Initial database scaffolding (#2)

* chore: Initial database scaffolding

This implements migrations and code generation for interfacing with a PostgreSQL database.

A dependency is added for the "postgres" binary on the host, but that seems like an acceptable requirement considering it's our primary database.

An in-memory database object can be created for simple cross-OS and fast testing.

* Run tests in CI

* Use Docker instead of binaries on the host

* Skip database tests on non-Linux operating systems

* chore: Add golangci-lint and codecov

* Use consistent file names

database/migrations/create_migration.sh

@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+cd "$(dirname "$0")"
+
+if [ -z "$1" ]; then
+    echo "First argument is the migration name!"
+    exit 1
+fi
+
+migrate create -ext sql -dir . -seq $1
+
+echo "After making adjustments, run \"make database/generate\" to generate models."