Change default path of language identifier binary

[jordiae]

Hi, I think having os.path.dirname(__file__) as the default directory for storing the binary would be a better default than "/tmp/fasttext-langdetect", since some systems might not have a working tmp directory. In any case, thanks for your library, it has been useful to me.

[zafercavdar]

Instead of replacing the default value, you can define FTLANG_CACHE environment variable dynamically before importing fasttext-langdetect like this:

import os
os.environ["FTLANG_CACHE"] = os.path.dirname(__file__)