Add fastutil primitive collections to reduce memory consumption

[pemistahl]

Several users reported in the past that Lingua would consume too much memory (e.g. #57). This is partly because of Lingua's design: Her language models are much bigger which is one of the reasons for her better accuracy compared to other language detection libraries.

However, as was tested in earlier versions of the library, the usage of the fastutil primitive collections, especially Object2DoubleMap, might help reduce the memory consumption of the language models and improve runtime performance.