WIK Fixed Bits vs Bytes issue

Fixes #337 

I'm not sure we want to also port the fix for the Culture. Humanizer supports different cultures. If I were to set my culture to `fr` I think I would prefer to see `10,5 KB` instead of `10.5 KB`. Let me know what you think, I can also port the culture fixes.

I added an extra unit test for the + operator overload. I also renamed the tests so they would fit more with the naming convention in Humanizer (`Add` vs `AddMethod`)