v0.4.0

Major configuration update with many new styling options.

• color.opacity - transparency for rectangles
• color.mid - three-color gradients (low -> mid -> high)
• color.param - use different field for color than display value
• size.inverse - low values get bigger rectangles
• size.param - size by different field than display value
• gap - control spacing between rectangles
• label.attribute, label.prefix, label.suffix, label.style - label customization
• value.attribute, value.prefix, value.style - value customization
• icon.param, icon.style - icon customization
• header.show, header.title, header.style - custom compact header
• card_style - custom CSS for the entire card