Fixed two major issues, the event loop and memory management

The event loop (now libev) now runs in a separate detached thread,
which is abstracted away from the user, who only calls a nonblocking
.start() method. This thread loops continously, alternating telling
Redis about asynchronous commands ready to send, and running one
iteration of the event loop, where all pending events are taken
care of. This greatly simplifies the user code.

Additionally, some clever tricker is implemented now to handle
memory management well with the templated command types. The
difficulty comes from the fact that we pass redis a void pointer
only, and must retreive everything from that (so, we can't use
shared_ptr for the whole thing). Thus, we use maps of void pointers
to their templated data structure pointers, where the memory address
of the pointer serves as the key.