Force redis-py version to use (2.9.1)

Some work has been done in redis 2.10 on the lock system that make some
of our tests fail (only `assertNumCommands` as the new lock system
use `lua`)
Make setup.py load requirements
Split requirements for py 2.6 and others

And make travis install dependencies via the package instead of requirements file
Add `future` to requirements
Apply stage1 of futurize

(but removed import of future in setup.py nad limpyd/__init__.py)
Apply stage2 of futurize and apply corrections

Correct with_metaclass calls

Do not inherit from `object`

Use str and bytes from future.builtins

Remove erroneous list() added by futurize

Use decode_responses=True when creating the Redis client
Small pylint/pep8 pass
Optimize iterators for 2.x and 3.x
Bump to version 0.2.0 and add notes about py 3.x
Temporary use a dev version of future
Merge pull request #86 from twidi/feature/python3-compat

Python3 compatibility