Increase HSL precision by default

[BaliBalo]

Somewhat related to #82, but I believe a change in defaults should be considered rather than an option ; at least in the color.minify function, which is used by default in tools like cssnano (this was reported in cssnano/cssnano#1515).

Conversions to HSL currently round all values to the nearest integer. This leaves it with less precision than the standard 8bit rgb format, used to store the color internally. This means some colors cannot be represented uniquely and get the same hsl values as nearby colors, and therefore the minification is not lossless (which seems to be the intent).
For example, rgb(14 14 14 / 50%) is converted to hsl(0, 0%, 5%, .5), which when converted back is rgb(13 13 13 / 50%).
I believe rounding HSL values to 1 digit precision would solve this.