Suggestion: significant_digits as alternative to decimal_places

[cederberg]

Sometimes I find it useful to print values with a minimum number of significant digits, instead of locking the number of decimals used. For example, when printing a system memory summary:

3.1 GiB (61.2%) free ∙ 677.1 MiB rss ∙ 1.3 GiB cache ∙ 5.1 GiB total

It is slightly easier to read when a minimum of two significant digits are used, instead of locking the number of decimals to 1:

3.1 GiB (61.2%) free ∙ 677 MiB rss ∙ 1.3 GiB cache ∙ 5.1 GiB total

Would this be an interesting addition to the library?