Refactor Agent for better performance and first class Trickle support

[kixelated]

performance: ice/Agent.getBestPair

This function should be virtually instant but it takes 1.34% of my program's cpu time.

The issue is the message passing required because of ice/Agent.run. It would be much faster if this class used a mutex instead of taskLoop.

[Sean-Der]

cpu.pprof.tar.gz

Here is a profile confirming. Most of our time is spend in sendto but that is another battle :)

[Sean-Der]

I have cleaned this up a bit, and now pion/ice isn't in the top 25. I am not going to work on this further.

I didn't end up removing .run, it is more then simple mutual exclusion it also allows cancellation of queued locks. I tried replacing things with a simple mutex, but ended up being more messy then I thought it would be.

For the cases where we want to return values from .run I have updated things to use atomics (instead of channels). .run itself is now blocking, and doesn't push the task across the channel. It instead calls the function directly.