mpb v5.2.1

New dependency on go-runewidth so decorators can use emoji or any double width runes, refer to complex example.

Added:

• func BarFillerMiddleware(middle func(BarFiller) BarFiller) BarOption
  refer to suppressBar example.
• decor.Statistics has new fields: AvailableWidth and Refill.

Minor breaking change:

• decor.Statistics now passed by value in decor.Decorator and mpb.BarFiller interfaces. If you don't use custom decorators, you're not affected.

Fixed #55 #66