feat(refacto): move everything in internal package

This allows to install katenary with `go install` and to clean up the
project folder.

internal/utils/hash_test.go

@@ -0,0 +1,13 @@
+package utils
+
+import "testing"
+
+func TestHash(t *testing.T) {
+	h, err := HashComposefiles([]string{"./hash.go"})
+	if err != nil {
+		t.Fatalf("failed to hash compose files: %v", err)
+	}
+	if len(h) == 0 {
+		t.Fatal("hash should not be empty")
+	}
+}