log.py
Removed log.py. Do we want any logging abstraction for ssl_crypto?

download.py
I think the crypto module is a good fit for download.py. But it uses TempFile from tuf.util which I'd rather not have in the crypto module. Actually, I am not really sure if we need this. Let's, kick it out for now.

conf.py
It would be nice to have a separate conf module that the crypto module can access but that lists all sorts of configurations for a specific project (toto or tuf). Plus maybe some config defaults in the crypto module.
We could use simple settings for this, or provide our own implementation.
See commit message for proposed solution.

sig.py
Uses TUF specific concepts, but parts of it could be interesting for a generic module. Maybe needs to be dissected.
More like a TUF signature util. Can be kicked out.

schema.py and formats.py
Same as for sig.py. Additionally, maybe schema and formats could be merged? Needs more review.
See crypto commit and toto commit for proposed solution.