Make chunk size configurable

[me21]

Currently the code reads files by 8 Kb chunks:

python-zipstream/zipstream/__init__.py

Line 310 in 961886f

buf = fp.read(1024 * 8)

Would it be beneficial to make it configurable?

[arjan-s]

To be honest, I don't know. The current code was already there when I forked the repo, so I'm not sure why this size was chosen. If you or anyone else cares about making this configurable, I'd be happy to accept a PR and make a new release for it.