Separated touch and delete
Apparently, the delete command does not really support a time parameter even though the code had support for it - https://github.com/memcached/memcached/blob/master/doc/protocol.txt#L254 Also, found that the expiry parameter is mandatory in touch - https://github.com/memcached/memcached/blob/master/doc/protocol.txt#L324. For these reasons, it makes more sense to use separate functions.
(Note - easier to review this change comparing to the version before my previous pull request - https://github.com/erankor/python-memcached/compare/794b02811d8c6fdad304955a4602fb1324270f95...e0ba0fc1fd30a3c1f1a06aea526d1e53f1850dfe)
just to mention that the function of flush_all should support an optional delay time according to the memcached protocol. I will make a pull request later, i think.
Thank you for the PR, I have updated it to match the new code and included it.