Minify style strings

[brandonkal]

This would appear to be an easy win to save some bytes.
Colors and other style strings can be made smaller in the final bundle:

const HoverRow = styled(StyledRow, {
  ':hover': {
    backgroundColor: 'rgb(229,       229,           229)',
  },
})

Becomes:

const HoverRow = styled(StyledRow, {
  ':hover': {
    backgroundColor: '#e5e5e5',
  },
})

Even lowercasing and shorthand whenever possible:
"#FFFFFF" -> "#fff"

[tajo]

Yea, this would be a nice addition since styletron is performance oriented. Assuming it would not add too much to the styletron's bundle size.

[re-thc]

0px can be set to 0. There's likely a whole set of rules that can be applied.