Refactored get and set.
Refactored get and set.

- Got rid of _prepare_key and _prepare_value
- Started using the base64 module directly
- Use the highest pickle protocol available
- Added a set_many method
- Added a delete_many method
- Added an expire method
- Made get_many return a dictionary as required

carltongibson/django-redis-cache,carltongibson/django-redis-cache,maikelwever/django-redis-cache,lucius-feng/django-redis,maikelwever/django-redis-cache,GetAmbassador/django-redis,zl352773277/django-redis,sebleier/django-dredis-cache,smahs/django-redis,issackelly/django-redis-cache,yanheng/django-redis,chripede/django-redis-cache,chripede/django-redis-cache