Change CWriter's Converter to an Assoc Type

[Pspritechologist]

The CTypeConverter doesn't follow the same pattern as the CWriter (implementing a trait of mostly default fns) making it very difficult to alter the functionality of. In addition, CWriter itself uses a static Converter type, disallowing altering it at all.
This pr changes the Converter CWriter uses to an associated type, allowing any type to be used in implementations of CWriter, whether or not they change any other logic.

I was going to do the same for the Python and C# backends, but I noticed their converters didn't implement Traits at all, so I left them alone. I'm happy to do the same for them if this change is favourable.

This is a breaking change of course since implementations of CWriter will need to add the new associated type (something default assoc types would fix 😔).

[Pspritechologist]

By the way, I was wondering if there was somewhere to discuss questions or thoughts about the library more casually than Issues. I didn't see any community chat linked to this project.
Would probably be a nice to have for something as deep as language bindings, especially since this project is designed to work very well with third party Crates.

[ralfbiedert]

Thanks! I'll look into this probably later tonight.

there was somewhere to discuss questions or thoughts about the library more casually than Issues

Right now "Discussions", but beyond that there's nothing else really.

[ralfbiedert]

Nm, just saw this is only a few lines.

[Pspritechologist]

Nm, just saw this is only a few lines.

Yeah, the diff is quite misleading :P
Just collapsing the trait def down onto the previous impl.

[Pspritechologist]

Right now "Discussions"...

I forgot that existed!