Add rules for combining words

[loket]

Currently, all words are combined without any specific rules (just a call to join()). However, this is not correct in Norwegian, and some of the letters should be concatenated in certain cases.

For instance, when combining the words "gebiss" and "skandale", the combined word should not be "gebissskandale" (3 "s"), but "gebisskandale" (2 "s").

[loket]

This would be partially solved by #60.