Add a --chunkSize param when using --asTask

[khalwat]

Add the ability to group the tasks into chunks for processing, so a separate queue job isn't created for every step, but rather every chunk.

This would allow for running a queue job that processes, say, 10 elements at once or such, and could reduce some unnecessary overhead.

[jalendport]

This issue has been moved over to our original Walk repo (per #3) - TopShelfCraft/Walk#3