Fix style: white space in exports and imports.

Better format ParagraphConstruction documentation.

Remove (~) operator from ParagraphConstruction.

The tilde operator was causing compilation errors with older versions
of GHC, possibly due to a conflict with the lazy pattern match syntax.

It has been replaced by a pure Haskell alternative that uses function
application.

Make SpanOptions a separate type.

Expose ParagraphConstruction.