Allow user specified line splitting in titles

Titles can be split at specified points with '\n' within the title
string. Titles segments which are still too long will still be split
over multiple lines in the normal way.

pygal/util.py

@@ -408,13 +408,14 @@ def split_title(title, width, title_fs):
     if not title:
         return titles
     size = reverse_text_len(width, title_fs * 1.1)
-    title = title.strip()
-    while len(title) > size:
-        title_part = title[:size]
-        i = title_part.rfind(' ')
-        if i == -1:
-            i = len(title_part)
-        titles.append(title_part[:i])
-        title = title[i:].strip()
-    titles.append(title)
+    title_lines = title.split("\n")
+    for title_line in title_lines:
+        while len(title_line) > size:
+            title_part = title_line[:size]
+            i = title_part.rfind(' ')
+            if i == -1:
+                i = len(title_part)
+            titles.append(title_part[:i])
+            title_line = title_line[i:].strip()
+        titles.append(title_line)
     return titles