Fix to avoid multiple listeners to mouseup in ExpressionHover.

Signed-off-by: Grant Skinner <info@gskinner.com>
SourceHighlighter now always draws on-pixel & with a minimum 1px gap between highlights.

Signed-off-by: Grant Skinner <info@gskinner.com>
Fixes to SourceHighlighter.

Signed-off-by: Grant Skinner <info@gskinner.com>