Add functionality to convert custom types

[lecafard]

Add some functionality to convert custom types, as well as allowing data to be injected during the conversion process.

Also reworked the registry into classes to reduce duplication, keeping in mind backwards compatibility.

[sinclairzx81]

@lecafard Hi, thanks for the PR. This one looks interesting (and sorry for the delay)

I'll need some time to sit down and properly review these updates (I am bit pressed with other projects atm), but did have a quick question regarding the rationale behind the additional data property to the Convert signatures.

I guess my initial thoughts is that metadata should be encoded and received via Schema only, but curious to know the thinking there.

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The registry updates look good here (that's some great thinking). I'll need a few extra days to properly sit down and go through these updates, but at a high level, these seem good. Just let me know your thoughts on the additional data parameter, and can pick things up in a few days.

Cheers
S

[lecafard]

Hi there, I originally added the data parameter as I had a use case where I needed to inject a specific encryption key that would be unique to the object being converted and couldn't think of another way to do that.

If there's a better approach, please let me know. I understand this is a rather niche use case, which might not be a good fit for this library.