add group for cache data
save the cache info
 array structure change
use timestamp as a flush key
Use strtotime instead of date format
use memcached to store the transient information
change the key name
tidy up
delete the variable assignment
tidy up
change if statement from empty($group_list ) to $group_list == false
Merge pull request #1 from stepcase/add-cache-info-WP-TLC

[Reviewd] add group for cache data