Fill changelong and prepare for v1.0 release.

Slightly decompose the Plain module.

Expose ParagraphConstruction.

Use internal library to hide non-public modules.

Move non-public modules into Internal namespace.

Add test for RTL text.

Use ICU to find line break boundaries.

Implement run splitting.

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.

Separate modules.