Find/create alternative to RichText for styling text

[Sub6Resources]

RichText works well, but it is not possible to have a widget inside of the TextSpan tree. This makes it difficult when tags like pre contain tags like img.

Creating or finding a widget that can take either a TextSpan or a Widget as a child would be a perfect solution and help to avoid the whole "supportedElement" "supportedInlineElement" discrepancy.

[Sub6Resources]

Currently being fixed as 0.5.0. This will be a major refactor and possibly affect all open issues and pull requests (but it's for a greater cause, a package that better embraces Flutter's "Everything is a Widget" philosophy).