Specify a Size without unit (e.g. for line-height) #79

It would be nice to be able to specify a number without a unit for Size Value.
I mean, does it makes sense to make a PR with such function?

num ∷ Number -> Size Value
num = Size <<< value

So it would be possible to write:

lineHeight $ num 2.0

Not sure if this looks good though 😂