Refactor and fix some issues with to_currency. Reduce code duplication. (#129)

* Refactor and fix some issues with to_currency. Reduce code duplication.

* Use unicode literals in uk testcase.

tests/test_lv.py

@@ -0,0 +1,15 @@
+# -*- encoding: utf-8 -*-
+from __future__ import unicode_literals
+
+from unittest import TestCase
+
+from num2words import num2words
+
+
+class Num2WordsLVTest(TestCase):
+    def test_to_currency(self):
+        self.assertEqual(
+            num2words('38.4', lang='lv', to='currency', seperator=' un',
+                      cents=False, currency='EUR'),
+            "trīsdesmit astoņi eiro un 40 centi"
+        )