Allow defining messages inside the component definition body

[mjstahlberg]

Allow defining messages inside the component definition body of the yaml document, so messages that are only relevant to a single component can be grouped more easily. This doesn't need to (but can, if it improves performance) have any semantic meaning, this issue just concerns the yaml layout.

[Kangz]

Shouldn't be too difficult to add, there might be name clashes though.

[mjstahlberg]

In that case an error could be thrown, I don't think overloading message names in any way would be a good thing.

[mjstahlberg]

I did not yet need this, retrieving the component in question and using direct method calls was sufficient.

[t4im]

Since messages are a form of inter-component communication, it seems this is a workaround to add convenience methods to specific Entitys. Perhaps it would be better to allow generating some form of delegator into the entities instead.

Something like:

entities:
    Fire:
        delegators:
            Extinguish: Igniteable
        components:
            Igniteable

FireEntity fire = new FireEntity();
fire.Extinguish(0); // -> fire.r_IgniteableComponent.Extinguish(0)

Of course this has the potential to be very verbose in the yaml file if one would be to add delegators to every entity. But so would be adding new message types for everything to components.