Merge pull request #4 from iborodikhin/master

XCache driver
Bugfixes and code style in XCache driver
Refactoring

Abstract cache driver was moved to Cache\Drivers namespace.
New protected methods doLoad, doRemove, doRemoveByTags and doTouch
Readme.ms update and removed unnecessary alias
Added support of key prefix for Memcache and XCache drivers
Composer version tag
New method to drop all items from cache
Fixed invalid response in MongoDB driver
Refactoring and new driver

Abstract classes moved to own namespace
New driver which uses redis extension added
Docs