Add writeln to print without breaking pbr

[kpcyrd]

I'm getting results that I need to print while the progress bar is on-screen. This currently breaks the progress bar. This patch also makes width() public which is needed to implement these sort of things outside of pbr.

[kpcyrd]

FYI: I've changed this to a different approach that doesn't require .width() and uses \x1B[2K instead to clear the line. This allows me to use colors with .writeln. This patch is still needed because I can't call .draw() from outside and therefore can't use max_refresh_rate because .tick() may not redraw the progress bar after I've printed a line.