Renamed files to make them more clear

Trying to figure out how to write. Might have to keep tables uncompressed for now.

writer_test.go

@@ -0,0 +1,16 @@
+package squashfs
+
+import (
+	"os"
+	"testing"
+)
+
+func TestWrite(t *testing.T) {
+	os.Remove("testing/test.sfs")
+	os.Mkdir("testing", os.ModePerm)
+	test, err := os.Create("testing/test.sfs")
+	if err != nil {
+		t.Fatal(err)
+	}
+	_ = test
+}