Restructure project

We previously didn't really had any structure in our project apart
from creating a new folder for each package in our project root.
Now that we have accumulated some packages, we use the well-known
Golang project layout in order to clearly communicate our intent
with packages. See https://github.com/golang-standards/project-layout

internal/api/health_test.go

@@ -0,0 +1,18 @@
+package api
+
+import (
+	"github.com/stretchr/testify/assert"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestHealthRoute(t *testing.T) {
+	request, err := http.NewRequest(http.MethodGet, "/health", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	recorder := httptest.NewRecorder()
+	http.HandlerFunc(Health).ServeHTTP(recorder, request)
+	assert.Equal(t, http.StatusNoContent, recorder.Code)
+}