feat(tox): add support for testing with tox

This adds notes in the README and a tox.ini file for use with the tox
test manager.

This helps greatly towards migrating python-memcached towards python
3.3+ compatibility.
refactor(reqs): separate deps in req files

To facilitate managing dependencies, they are now listed in
requirements files.

This also simplifies the tox.ini file.

A dependency on six was added to aid with porting to python 3.
fix(setup): use new reqs files
fix(tests): use print() for py3
memcache: get closer to py33 compat, style fixes

The following changes were systematically applied throughtout:

* print 'thing' -> print('thing')
* except Exception, msg -> except Exception as msg:
* pep8 fixes:
    * lines too long (>79 characters)
    * imports out of order
    * importing functions from a module: zlib, threading
    * comparison to None, e.g., x == None vs. x is None
    * spaces between/after/before operators
* dict.iterkeys -> six.iterkeys(dict)

The following are BREAKING changes:

* zlib is required now
* minimum Python version is 2.6 (io module, exception syntax)
fix(memcache): import print function
fix(ignores): .coverage
cmemcache_hash: Encode key to bytes
Use six.iteritems
check_key: Auto-convert unicode keys to bytes for better Python 3
compat

It would be a bit of a pain (and ugly) in Python 3 to have to prefix all
literal keys with the "b" literal notation for bytes.
setup.py: Duplicate version so we don't have to import memcache

This will fail if memcache imports dependencies that are not installed
yet, like `six`.
Merge pull request #1 from msabramo/py33_fixes

Py33 fixes
Merge branch 'py33_fixes' of https://github.com/cabrera/python-memcached into cabrera-py33_fixes

Conflicts:
	README.md
	memcache.py
	tests/test_setmulti.py
Removing debug print that slipped in.
Python3 fixes
Fix travis configuration
Merge remote-tracking branch 'origin/py3-fixes'