add healthcheck route

cmd/api/main.go

@@ -44,6 +44,8 @@ type application struct {
 	logger     *log.Logger
 }
 
+var version = "0.1.0"
+
 func openDB(cfg config) (*sql.DB, error) {
 	db, err := sql.Open("sqlite3", cfg.db.dsn)
 	if err != nil {