Reimplemented xxHash after discussion with @msteindorfer to improve our IntegerValue hashcode
Reimplemented xxHash after discussion with @msteindorfer to improve our IntegerValue hashcode

We tend to have small numbers, and this provides a strange distribution in the `.hashcode()`

usethesource/rascal-value,cwi-swat/pdb.values,cwi-swat/pdb.values