Connection registry

Now we can use leak sanitizer. Yay!

src/connection.cpp

@@ -5,6 +5,8 @@
 #include <errno.h>
 #include <limits.h>
 
+// TODO fix up this whole thing
+
 std::unique_ptr<Connection>
 Connection::createForServer(struct sockaddr_storage addr, int fd, int64_t id,
                             ConnectionHandler *handler,