Add test for Devanagari.

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It has been replaced by a pure Haskell alternative that uses function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

Test forming and breaking ligatures.

Fix comment syntax.

Add line wrapping tests with spans.

Make SpanOptions a separate type.

Move non-public modules into Internal namespace.

Add test for RTL text.

Test line splitting with many runs.

Add ignored prefixes and suffixes to test data.

This ensures that implementation does not rely on the texts having zero
offset inside their byte arrays.

Implement line breaking on code point boundaries.

Implement absolute line heights with half-leadings.

Use infix operators for constructing test data.

Implement "plain" interface.