Fix path for asset storage (#144)

Define locations for keys and secondary zones, 'n stuff.

Add a bunch of tests as well.

middleware/test/file_test.go

@@ -0,0 +1,11 @@
+package test
+
+import "testing"
+
+func TestTempFile(t *testing.T) {
+	_, f, e := TempFile(t, ".", "test")
+	if e != nil {
+		t.Fatalf("failed to create temp file: %s", e)
+	}
+	defer f()
+}