Generators barf bag

[nozavroni]

This issue will just be a place for me to barf ideas about how best to utilize generators within this library.

So far this library doesn't make use of generators whatsoever, which is really a shame. I think it's time we introduce generators somehow. I have a few ideas for this...

Generator Collection Decorator

$coll = new Collection(['blba','babas','asdsad','bleeebloo',3,4,5,6]);
$gencoll = new GeneratorDecorator($coll);
// now $gencoll can be used exactly as you would use $coll, only now its values are yielded

But no that wouldn't work because generators can only go one way (and they can only be looped over once). So what would be a more appropriate use for generators here? Well there's this: #80.

Another good use of generators would be for things like #46. When doing things like this:

$coll = CollectionFactory::fromGenerator(function() {
    foreach (range(1,20) as $val) {
        yield $val;
    }
});
// or... 
$coll = MySQLFactory::fromQuery($sql);