Print relative times with decimal numbers

[MenoData]

CLDR-patterns for relative times are only available with one (or zero) placeholder for the amount. This could be a decimal number, however. Actually it is just a rounded down integer.

• A new overloaded printRelative()-method in class PrettyTime with an extra int-parameter indicating the count of decimal digits would be sufficient to reach this goal.
• An extra configuration method for the decimal separator to use would be a good supplement, too.

Using decimal numbers might imply changes in the plural rules (needs investigation).