~jaro/balkon

ref: 13f4f8e765e5858c8869af76894b52d8a4d5bf6a balkon/src/Data/Text/ParagraphLayout/Internal/Plain d---------
Refactor lineNumbers into a common module.
Refactor pagination to allow rich layout.
Separate interface-independent constants.
Add user data to spans.
Separate internal plain Paragraph/ParagraphLayout.