A start at a multi-version release pattern.

This commit moves everything that was in the kitchen/ source dir into a new
kitchen2/kitchen/ source dir.  Eventually, we'll merge the py3port branch
into a kitchen3/kitchen/ source dir parallel to it.

I added both source folders to ``MANIFEST.in`` so when we create a tarball
with ``python setup.py sdist``, **both** source directories will be
included -- kitchen2 and kitchen3.

When the user downloads and installs the package with ``pip install
kitchen``, it will download the tarball with both sources, unpack it, and
run the single setup.py.  setup.py has new logic in it now that will detect
if the user is running python2 - if it is, then it will install kitchen
from the kitchen2/ directory.  If they're running python3 it will install
kitchen from the kitchen3/ directory.

Note that, the imports for users do not change at all.  For both python2
and python3, kitchen can still be accessed with

```python
>>> import kitchen
```

/cc @abadger, @rkuska