Use first line of sourcedoc as title

tests/test_text.py

@@ -0,0 +1,21 @@
+from sourcing import text
+
+def test_find_newlines():
+    sample = ''
+    assert list(text.find_newlines(sample)) == []
+
+    sample = 'aaa\nbbb\nccc\n'
+    assert list(text.find_newlines(sample)) == [4, 8, 12]
+
+def test_iter_lines():
+    sample = ''
+    result = list(text.iter_lines(sample))
+    assert result == []
+
+    sample = 'aaa\nbbb\nccc\n'
+    result = list(text.iter_lines(sample))
+    assert result == [(0, 'aaa\n'), (4, 'bbb\n'), (8, 'ccc\n')]
+
+def test_first_non_empty_line():
+    assert text.first_non_empty_line('') is None
+    assert text.first_non_empty_line('  \n  \n') is None