~jaro/balkon

ref: 6e011c818a62f3d3ae7554f67f24fc8f3abf031b 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.