Add __init__.py to make pip installable modules

[cadolphs]

Trying to run another project in a remote environment, and that needs to pip-install the taming transformers repo. The original project uses conda and pip install -e and, presumably, is meant to work locally.

In my case, pip install via invoking setup.py and find_packages() doesn't actually find the modules, such as taming.modules.vqvae. That's because find_packages() only treats a subfolder as a package if it contains an __init__.py. Otherwise it's just considered a "namespace package".