Improve fairness of TaskExecutorDistributor

[threadly]

Improve fairness of TaskExecutorDistributor

[jentfoo]

Because other fairness strategies would have performance impacts. And in addition I am not sure what use cases we would be trying to solve with additional strategies, I am going to wait on implementing this enhancement.

If anyone would like to see this, please post a comment about what fairness strategy, and why you would like to see it. That way I can be sure to implement something that will be useful to lots of people.

Right now the fairness strategy of limiting the amount of runnables per key at a time (possibly in combination with a sub pool), should solve most peoples use cases.

[jentfoo]

I marked this for version 2.0.0 since to do this cleanly, we would have to make non-backwards compatible changes.

Depending on feedback, and how I feel about this as we get closer to 2.0.0 we may or may not want to include this additional functionality. But still marking for 2.0.0 milestone as that is the earliest we can do this (of course 2.0.0 can occur when ever want it to).

[jentfoo]

I am going to go ahead and close this as wont fix. This could still be done, I have a branch on from my local fork for 2.0.0, but worry this complicates things more than it is worth. As I stated above, if anyone is interested in something like this, let me know, we can re-open this. But I hate to add a builder pattern right now when the need is not clearly defined, and it adds complexity that is different from everything else in this project right now. If we have a need for more builders in the future, I will likely do this then as well.