Adding failing test to demonstrate issue with time_series plot x axis labels

tests/test_time_series.py

@@ -0,0 +1,17 @@
+from svg.charts import time_series
+
+def test_field_width():
+	"""
+	cking reports in a comment on PyPI that the X-axis labels all
+	bunch up on the left. This tests confirms the bug and tests for its
+	correctness.
+	"""
+	g = time_series.Plot({})
+
+	g.timescale_divisions = '4 hours'
+	g.stagger_x_labels = True
+	g.x_label_format = '%d-%b %H:%M'
+
+	g.add_data({'data': ['2005-12-21T00:00:00', 20, '2005-12-22T00:00:00', 21], 'title': 'series 1'})
+	g.burn()
+	assert g.field_width() > 1