Allow skipping properties in LazyLoadingGhost for partial initialization

[Ocramius]

In order to use lazy loading ghost objects in different contexts, we may need to allow partial initialization as well.

One way to do that is to generate different proxy classes for different sets of properties being requested to be skipped from following lazy-loading semantics.

A possible API implementation may look like following:

class LazyLoadingGhostFactory extends AbstractLazyFactory
{
    public function createProxy(
        $className,
        \Closure $initializer,
        array $options = []
    ) {
        /* ... */
    }
}

A possible usage may be like following:

// no properties skipped
$proxy = $factory->createProxy('Foo', function () { /* ... */ });
// skip privateProperty, protectedProperty and publicProperty
$proxy = $factory->createProxy(
    'Foo',
    function () { /* ... */ },
    ['skippedProperties' => ["\0Foo\0privateProperty", "\0*\0protectedProperty", "publicProperty"]]
);

In order to avoid class inheritance collisions, values of 'skippedProperties' are PHP's internal logical property names (used for array serialization).

Ping @malukenho want to give this a shot?

[Ocramius]

Handled in #221