v0.7.0

Many new updates:

• Now uses purescript-colours, which fixed #22 (@sharkdp)
• Added viewport units (@menelaos)
• Prefixed animation and keyframe support (@cryogenian)
• box-sizing (@Podlas29)
• More element selectors (@menelaos)
• Semigroup instance for CSS (@menelaos)
• Flexbox module (@menelaos)
• Fuller implementations for the Background and Gradient modules (@menelaos)
• String rendering fixes (@paluh)
• white-space (@adarqui)