Crosslink detection: consider taking simple sound changes into account

[stscoundrel]

Simple example: from Old Norse word "hvalr", there would later be descendant "hval", simply by dropping the ending r. This would be common pattern that may be easy to recognize, allowing links from west norse to east norse words (=west generally kept -r longer)

See if this kind of feature:

• Produces respectable amount of crosslinks without too many false positives. Should there be too few, we may be better off just using manual overrides
• Has decent enough performance. Naive way could easily end up doing quite a bit of comparisons, as there are some 120K+ entries in the dictionaries.

[stscoundrel]

Another common one seems to be writing eth of western dialects as "dh" in Old Swedish. For example, various words containing faðir reliably turning into fadhir