Create an installable python package

[konstin]

Hi!

I'd like to integrate this model in another python package (bio_embeddings). This requires that the source directory is named after the module and that pip can build a wheel for the repository. I've added both things in this pull request. Unfortunately, this means that the pretrained model as they are no can't be loaded anymore, as it doesn't find src anymore and would need to be migrated. I wanted to propose those changes anyway since I use them to integrate this model into bio_embeddings.