This commit makes rewrite explicitely match items using the .lower() function
instead of using Pythons builtin re.I flag.
This is required as the re.I flag only allows for case-independent pattern
matching with ascii chars. Even worse, the pattern is stored in lowercase when
using re.I, but the value to be matched isn't lowercased.
Example:
[rewrite]
artist Сергей Васильевич Рахманинов: Sergei Rachmaninoff
