Add support for `unicode-range` wildcard minification

[strarsis]

Some unicode-ranges can be even further minified into a wildcard in CSS output (and possibly also in the Unicode Range Interchange tool):

E.g. this unicode-range unicode-range: U+40-4F;

Can be further minified to: unicode-range: U+4?; (As ? stands in for 0-F.)

[strarsis]

Closed in favor of https://github.com/bramstein/characterset/issues/5.