Moved model classes in model package

[afester]

This commit moves the model related classes into a separate "model" package. Meanwhile, there are plenty of classes in the "org.fxmisc.richtext" package, both UI related (with a strong dependency on JavaFX Node classes to create the scene nodes) and model related. Separating out the model classes would definitely help to understand the overall structure of the editor, specifically when getting started.
The drawback might be that some classes and methods had to be made public rather than package scoped, but I think this is reasonable.
Any comments are welcome ...

[TomasMikula]

The change makes sense to me. I think it is a much better separation than what we used to have before: the main package and the skin sub-package, where in the main package we had a mixture of model and some parts of the view, and skin contained the rest of the view.

Can you also move model-related test classes to the model subpackage?

We should try to avoid circular dependencies between packages. Can we make model independent of the main package (i.e. not import anything from there).

You will also need to resolve the merge conflict.

[afester]

Hi Tomas,
I have updated this branch to the head of master. I had already solved the merge conflict, and made sure that there are no dependencies from classes in the model package to other RichTextFX classes. The model package is now self-contained. I also moved the model tests to the org.fxmisc.richtext.model package. Please let me know if anything additional is required ...

[TomasMikula]

Why did this need to become public?

[afester]

Its used in StyleClassedTextArea:

SuperCodec.upCast(SuperCodec.collectionListCodec(Codec.STRING_CODEC)),
SuperCodec.upCast(SuperCodec.collectionListCodec(Codec.STRING_CODEC))

[TomasMikula]

Other than the SuperCodec made public, looks good to me 👍

[TomasMikula]

👍