Provide a "unique request id" in stex.log

[thejollyrogers]

When a stex application recieves a request, it would be nice to attach a unique id to every log that arrises from that request. that way logs could be tracked by request id. the asynchronous nature of node makes this hard as you lose context in the callback after the event loop.

here's a potential solution or model we could use https://datahero.com/blog/2014/05/22/node-js-preserving-data-across-async-callbacks/

Ideally most of the functionality would be abstracted into Stex, and all the client would need to do is add some stex speicific middleware to their request chain, and any further call to Stex.log will automatically add that request id to the log.