Fix documentation: references to local names.

Separate internal plain Paragraph/ParagraphLayout.

Expose text slicing functions.

Decompose text slicing.

Integrate BiDi reordering.

Implement BiDi resolved level reordering.

Represent lines with non-empty lists.

We can do this because we removed lines with zero size.

Remove lines with zero size.

These lines would otherwise affect line numbering.

Do not re-export through the Plain module.

Move paragraphSpanBounds to the correct module.

Clarify comment about BiDi.

Correct comment about fragmentation.

Fix style: long lines.

Fix style: small Prelude imports.

Fix style: external vs internal imports.

Fix style: white space in lambdas.

Fix style: white space around operators.

Fix style: white space in exports and imports.

Fix style: bullet points in comments.

Fix style: non-ASCII characters in comments.