Refactor: split into multiple files

Given the size of the assignment, having everything in the same file was
OK. However, splitting into different files is a good option for better
maintainance once this API grows, and now is a good time to do it before
it gets more complicated.

README.md

@@ -15,12 +15,26 @@ This project uses Leiningen. Assuming you already have Leiningen installed,
 running the API should be as easy as cloning the repo and issuing `lein run`. By
 default, the server listens on port 3000.
 
+## Structure
+
+The source code lies in `/src/yohoho` and is structured as follows:
+
+* `app.clj`: ring app and main entrypoint
+* `config.clj`: configuration (database and HTTP server)
+* `db.clj`: functions that directly interact with the database
+* `handlers.clj`: route handlers
+* `helpers.clj`: the infamous file that holds function that are useful but
+  couldn't fit anywhere else
+* `routes.clj`: API routes
+* `schemas.cls`: Malli schemas used for validation
+
 ## Library choices
 
 * `reitit`: for handling routes
 * `jetty`: web server
 * `muuntaja`: JSON handling
 * `next.jdbc`: database interface (SQLite)
+* `malli`: validation
 
 ## Documentation links