Allow rounding option

This option allows users to limit the default precision to what’s defined in precision, but doesn’t round the number if the rounded number isn’t equal to the number itself. This may sound a bit vague, so let’s demonstrate this with an example:

Let’s assume you have configured precision: 5 and allowRounding: false:

• calc(100% / 3) will output calc(100% / 3) because calc(100% / 3) != 33.33333%
• calc(100% / 4) will output 25% because calc(100% / 4) == 25%

What’s the advantage? We never have rounded numbers which can cause issues like https://github.com/twbs/bootstrap/pull/27374 and we don’t have expressions like calc(100% / 4) that can be simplified.

PR: https://github.com/postcss/postcss-calc/pull/61

[MartijnCuppens]

precision: 'safe' would still need some kind of precision. Lets say for some reason the generated value would be: 15.35153465435186437435513 (and this is the exact number, no numbers after the last 3). That’s a pretty long number, probably something you don’t want. This is why I split precision & allowRounding.

[alexander-akait]

@MartijnCuppens Maybe we can do better:

- precision: false - disable precision
- precision: 5 - 5 characters
- precision: 'safe' - as you want in this issue

?