Use internal library to hide non-public modules.
Move non-public modules into Internal namespace.
Use ICU to find line break boundaries.
Lay out Runs independently of Spans.
Implement absolute line heights with half-leadings.
Upgrade Fragment to contain pen position.
Use infix operators for constructing test data.
Implement "plain" interface.
Create "plain" interface.
Add module for working with rectangle coordinates.
Clean up and update package description file.
Automatically discover test specs.
Separate tests by module.
Add unit tests for spanToRuns.
WIP version with WIP interface.