pattern.de.singularize() produces wrong results for suffix "en"

[jnns]

https://github.com/clips/pattern/blob/master/pattern/text/de/inflect.py#L316

The default pattern is to cut off the suffix en from plural nouns to return the singular but this does only work in some cases, not for one of the following:

• Löwen → Löw
• Konserven → Konserv

[tom-de-smedt]

Overall, singularization is about 80% correct, which is not bad. It also means that it will get 2/10 words wrong; these will stand out. I added some extra rules to the algorithm. If you have more examples, please let me know! Tom