Add extensible filter for invisible lines.

Store default level in BiDiLevels.

This will be required for handling empty text sequences.

Prepare for vertical-align in BoxOptions.

Implement calculation of safe paragraph width.

Refactor lineNumbers into a common module.

Update changelog on paragraph alignment options.

Test with AlignStart by default.

Test centred paragraph.

Allow paragraphRect without point 0,0.

Test right-aligned paragraph.

Add start/end paragraph alignment.

In the future, when the paragraph direction is not explicitly set,
start/end options will allow alignment to change line by line,
whereas left/right alignment will be constant.

Add centre/right paragraph alignment.

Internally mark hard line breaks.

Internally allow splitting texts at endpoints.

This is required in order to preserve a hard line break at the end of
the input.

Internally support text breaks in ascending order.

Intended as a workaround to `breaksRight` not including the status of
the end-of-text break.

Separate split list functions into a module.

Fix terminology for box layout bounds.

Test handling of empty lines.

Make RTL text overflow the left paragraph edge.

This behaviour is consistent with CSS Text Module Level 3.

BREAKING: Previously, all text would overflow the right paragraph edge,
regardless of text direction.

Test mixed line height.