Basic Implementation Making Queue Size Configurable by Workers

[gxuu]

I've rolled a basic solution according to the requirements outlined in issue #51. I welcome any comments and advice to further improve the program.

[gxuu]

More detail in the discussion of issue #51. This is not ready to merge and I plan to make improvement after receiving feedback.

[gxuu]

UPD:

This commit refactors the worker queue handling and balance algorithm. The changes include:

• Modified the original function signature instead of introducing new APIs.
• Updated the entry_point/ implementation to use the new functions.
• Removed references to per_worker_queue_size.
• Allowed worker queue sizes to be initialized externally, both as command-line arguments and function parameters.
• Revised the implementation for symphony workers.
• Modified the balance algorithm.
• Updated all test implementations to use the new functions.

Note on design:

• per_worker_queue_size is probably worth keeping. It can be used as default when queue sizes are not provided. My opinion is that the name is confusing, and therefore I removed it for now.
• Symphony CLUSTER seems to have only a single worker instead of a cluster. I am not sure whether this is intended or a work in progress. For now, the worker in symphony cluster only have one queue size.
• worker queue sizes doesn't have a default value for now, but it might be worth adding one. Otherwise, the code looks nasty.

I would like to receive one more round of feedback before cleaning up the mess. That said, I think all the changes that needs to be done are done.

gxu