neubot_asyncio/futures.py: fix import statements
neubot_asyncio/transports.py: fix import statement
neubot_asyncio/connect.py: fix two logging statements
neubot_asyncio: implement limited create_connection()
neubot_asyncio/__init__.py: export more stuff
neubot_asyncio: more correct and simple Future emulation
{neubot_asyncio => net}/connect.py

The connect.py module should use neubot_asyncio but should not
be part of the neubot_asyncio module.

With this commit I'm reversing the trend of putting all the files
in neubot/ directory.

To help people understanding how Neubot works, I'll commit to be
more tidy than I used to be.