Add the ability to specify the max number of waiters for a resource
pool, this provides a more efficient way of avoiding waiters for a
resource pool continually rising.
This commit also improves the destroy behaviour.
Mostly to no longer sleep in the main fiber. Now the main fiber just
spawns other fibers when it would previously block on put-operation
and these other fibers communicate back to the main resource pool
fiber when necessary.
This should mean that the resource pool is more responsive.
