Basic structure of the project

- Added a model with in-memory database, and routes, controller and
middleware to enable making initial CRUD calls to endpoints;

- Added jest and an initial test.

src/app.ts

@@ -1,11 +1,22 @@
 import express from 'express'
+import topicRoutes from './routes/topicRoutes'
+import { errorHandler } from './middleware/errorHandler'
+
 const app = express()
 const port = 3000
 
+app.use(express.json())
+
+// Routes
 app.get('/', (req, res) => {
   res.send('Hello World!')
 })
 
+app.use('/api/topics', topicRoutes);
+
+// Global error handler (should be after routes)
+app.use(errorHandler);
+
 app.listen(port, () => {
   return console.log(`Express is listening at http://localhost:${port}`)
 })