Asyncio

Working asyncio and aiohttp implementation, replacing the ``requests`` library (for talking to bitcoind's multiple RPC threads asynchronously).  You should use python 3.4.1 or newer due to this bug: http://bugs.python.org/issue20275 which results in spammy logging with ``--verbose``.  aiohttp is relatively new and you should install it from git for now. https://github.com/KeepSafe/aiohttp

It may be possible to get this to work under python 3.3 as well, but asyncio must be installed as an external package.  (It comes with python 3.4).
Can we use variables in `config.py` here?