Fixed Windows compilation errors and memory leak

Fixed Windows compilation errors introduced by https://github.com/zeromq/aziomq/pull/8
and memory leak discussed in https://github.com/zeromq/aziomq/pull/9#discussion-diff-20735727
Solution with only one ctor accepting T by value is great if you can be sure that T will be always a movable type. (Otherwise you need two overloaded ctors.). If you are 100% sure, let's go with one ctor.