Added AsyncRPCQueue::closeAndWait() so rpcserver can block on worker threads when shutting down.
AsyncRPCOperation is no longer copyable - copy constructor and assignment operators now private.
Refactoring: renamed methods, renamed member variables
Tidy up: comments, const, size_t, braces
Simple implementation does not try to optimize coin or note selection.
Caller can send from a taddr or zaddr to multiple recipients.
Currently only one of the recipients can be a zaddr.