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/db_memory.go

@@ -0,0 +1,19 @@
+package database
+
+import "context"
+
+// NewInMemory returns an in-memory store of the database.
+func NewInMemory() Store {
+	return &memoryQuerier{}
+}
+
+type memoryQuerier struct{}
+
+// InTx doesn't rollback data properly for in-memory yet.
+func (q *memoryQuerier) InTx(ctx context.Context, fn func(Store) error) error {
+	return fn(q)
+}
+
+func (q *memoryQuerier) ExampleQuery(ctx context.Context) error {
+	return nil
+}