• expose a new argument nrows=None
  • default: auto-detect terminal height with some sensible default such as 20 (similar to ncols)
• hide bars if n < total and pos >= nrows
  • completed/close()d bars will ignore nrows and just print according to leave
• TODO: link related issues

This fixes issues where there are more nested bars than room for on a screen.

Cross-platform auto-detection compatibility will be at least as annoying as is for ncols.