~jaro/balkon

ref: e84f038725a11b56cb08d1bf047f15adb5e0070c 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.