Prevent fractions of thumbnails.

[gregdick1]

The fractional thumbnail on the right end of the bar was really bugging me, so I set out to try and prevent fractional thumbnails by calculating the closest width necessary to perfectly fit the thumbnails into the bar. Some thumbnails will end up with a picWidth +1 larger than others to make up for fractions. This works regardless of what picWidth you set.

Old bar with fractional thumbnail on the end (screen taken from readme.md)

New bar with no fractional thumbnails

(note the difference in bar lengths is just due to how the screenshots were taken. It's not from any changes in the code)

[dimohamdy]

@andrei200287 where are you please check pull requests