Added __init__.py to make fragfold/src a module

[Ferryistaken]

The file __init__.py isn't included in fragfold/src, meaning that it's not recognized as a python package.

Also, I had to force add this file by running:

git add -f fragfold

And then adding the specific file. For some reason when just trying to git add fragfold/src/__init__.py I got:

The following paths are ignored by one of your .gitignore files:
fragfold
hint: Use -f if you really want to add them.
hint: Disable this message with "git config advice.addIgnoredFile false"

However I couldn't figure out where in the .gitignore it's ignored. git check-ignore -v fragfold doesn't return anything.