Lists: add support for various list styles other than the default

This was inspired by the CLDR 32 release notes:

> New “disjunctive” list style (eg “a, b, or c”)

1 files changed, 7 insertions, 0 deletions

diff --git a/tests/test_lists.py b/tests/test_lists.py
index bd297ec..e843a63 100644
--- a/tests/test_lists.py
+++ b/tests/test_lists.py
@@ -1,4 +1,6 @@
 # coding=utf-8
+import pytest
+
 from babel import lists
 
 
@@ -12,3 +14,8 @@ def test_format_list():
         (['string1', 'string2', 'string3', 'string4'], 'ne', u'string1,string2, string3 र string4'),
     ]:
         assert lists.format_list(list, locale=locale) == expected
+
+
+def test_format_list_error():
+    with pytest.raises(ValueError):
+        lists.format_list(['a', 'b', 'c'], style='orange', locale='en')