Increase key to 64-bytes for PSR-16 Compatibility

[spekary]

http://www.php-fig.org/psr/psr-16/ implements a common interface for caches. One requirement is that a cache that implements the interface must be able to support a 64-byte key. I am not sure why YAC chose a 48-byte key, but if it is not difficult to increase the key size, the community would benefit.

[laruence]

hmm, the problem here is, if I increase the key from 48 to 64, the conflicts may raise.... I will try do some tests.. thanks