Chained setting of data to component

[danielkcz]

In the light of upcoming PR #15, this is another change that would simplify things. With component registry it's much easier to add component into entity, but since it has no data, it might be less useful. Let's improve it like this.

entity.add('personComponent')
    .set('firstName', 'Daniel')
    .set('lastName', 'K.');

This would obviously require to introduce small breaking change since entity.add returns entity instance itself. In my opinion it's not that useful as having component returned.

Adding the set method on component instance might be also seen as a step toward the future and perhaps implement some more sophisticated ways of setting component data.