Add an SQL DB abstraction layer

Because what self-respecting Enterprise(R) project doesn't have
one of those?

src/sql/api.ts

@@ -0,0 +1,19 @@
+import * as sql from "sql-bricks-postgres";
+
+export type Id<T> = bigint & { __id: T };
+
+export interface Row {
+  [key: string]: any;
+}
+
+export interface Transaction {
+  modify(stmt: sql.Statement): Promise<void>;
+
+  fetchRow(stmt: sql.SelectStatement): Promise<Row | undefined>;
+
+  fetchRows(stmt: sql.SelectStatement): Promise<Row[]>;
+}
+
+export interface DataSource {
+  transaction<T>(callback: (txn: Transaction) => Promise<T>): Promise<T>;
+}