Fix panic in Memory store when deleting. Write lock wasn't acquired

IF file could not be opened because it doesn't exists, return a "Cache

miss" error

use os#IsNotExist to detect non existent files Don't open files just …

…to check if it exists, use os

#Stat instead

updated changelog [ci skip]

remove glide

updated changelog

Prevent garbage collection blocking other ops... GC is now being run …

…inside of a seperate goroutine

Redis adapter should make use of the default prefix when the adapter …

…is automatically registered.

Allowed third party cache stores integration

- Fixed race condition in tests for the memory and filesystem stores

Improvements to the memory store as to how data are stored