Implement wpool:broadcast/3 function

[harenson]

The idea is to implement a function that works like wpool:broadcast/2 and it receives a third parameter that would be a broadcast_strategy.

The default (not necessarily has to have that name) one will work exactly as broadcast/2 works, the other broadcast_strategy will have to queue the message and once the queue gets to this message it will have to handle it specially, I mean, it won't send this message to the first available worker but to all of them.