Zend_Cache_Backend_Redis with support for tags

! proof of concept

FEATURES

• Uses redis PECL extension (https://github.com/owlient/phpredis)
• The use of tags is simulated by using the “set” datatype available in redis.

KNOWN ISSUES

• Some methods are not implemented yet
• No proper tag cleanup is done on item expiry
• Needs to be unit tested