Design a good way to pass transport options to child PTs
Client transports get their k=v options from the SOCKS parameters, which is given in the Bridge line. Server transports get their k=v options from ServerTransportOptions.
We need to define ways for fog to pass these options down to the relevant child.
For example, one basic syntax would be, if fog receives an option of the form "fog-child-n-k=v", it passes "k=v" as the option (either SOCKS or ServerTransportOptions) down to the nth child PT in the chain. (This may not be the best idea; the consequences should be examine before we commit to this.)
This must be documented as a public API of fog.