bin: Admit more than 2 encoder passes
bin: Admit more than 2 encoder passes

Triple-pass can be implemented with the somewhat awkward:
rav1e --first-pass pass.1 -b NNN -o /dev/null seq.y4m
rav1e --second-pass pass.1 --first-pass pass.2 -b NNN -o /dev/null seq.y4m
rav1e --first-pass pass.2 -b NNN -o seq.ivf seq.y4m

xiph/rav1e,xiph/rav1e