Add missing move constructor for connector template

[mcopik]

The main template class of tcp_connector is missing a move constructor - it is in the base class, but not in the derived class.

This makes it impossible to use connections with std::vector, as it requires a move or a copy constructor.

#include <vector>

#include <sockpp/tcp_connector.h>

void foo()
{
  sockpp::tcp_connector conn;
  std::vector<sockpp::tcp_connector> connections;
  connections.push_back(std::move(conn));
}

[fpagliughi]

Oh, of course. Thanks!