Add Python 3 compatibility

This PR makes streamparse Python 3 compatible (issue #9) by:

- Using six for `iteritems` and `reraise`
- Adding `from __future__ import absolute_import, print_function, unicode_literals` to the top of nearly every `.py` file.
- Replacing the few remaining `print` statements with `print` functions.
- Explicitly decoding/encoding all strings sent to/from spouts and bolts using UTF-8.
- Adding 3.3 to `.travis.yml`.
- Relying on a [Python 3.3 compatible fork of Fabric](https://github.com/pashinin/fabric/tree/p33) referred to in fabric/fabric#1050 until the official Python 3 compatible version of Fabric [comes out in the next few weeks](https://twitter.com/bitprophet/status/484081844162289665).
- Removing `unittest2` from `test_requires` when on Python 3.

I also fixed a few pylint issues and other general correctness things like:

- Eliminating `[]` and `{}` as default arguments as to avoid [this nonsense](http://effbot.org/zone/default-values.htm).
- Stop importing `streamparse` for `__version__` in `setup.py` to fix [potential issues where the user doesn't have all prereqs already installed](http://stackoverflow.com/questions/2058802/how-can-i-get-the-version-defined-in-setup-py-setuptools-in-my-package).
- Switch to using `README.rst` instead of `README.md` and made `setup.py` automatically use that as the `long_description` for PyPI.

I have not extensively tested this beyond making sure all the unit tests pass on 2.7 and 3.3 on Travis, so let me know if I missed something.
I'm just being extra cautious. On Python 3 you [can't write `bytes` directly to `sys.stdout`](https://docs.python.org/3/library/sys.html#sys.stdout), but you can write to the underlying buffer, which is what I'm doing.

I cannot for the life of me find where I saw it, but somewhere I had read that when writing to the buffer directly, you should always flush first in case there are `str` things buffered (from using `sys.stdout.write` directly). In our case, I'm not sure that would ever happen, but I was just trying to be safe. 

We can certainly take it out if you think it could cause performance issues or something.