Don't block the thread calling send

[kornstar11]

Idea is to run an internal pool of threads so that blocking operations don't block the callers... is this a good idea?

Many changes here, some maybe not so good.

• For one the life times have been removed, everything is now owned. This may mean additional copies for implementors. The reason for the lifetime removal was to allow for the data to be shuttled off to a different thread, and since we enforce 'a life time on the data and the Sender it maybe it difficult to refactor code that used this lib, if we wanted to run in a seperate pool.
• We add a mutex on the sender, internally ConnectedServer uses a Cell which is not thread safe, so we threw a mutex around it... EZ.

I am pushing these, since they may be interesting, but I am not sold that this is hte best way forward.