(optionall) zero pad the filenames of the output PNGs

[nigelmegitt]

In the hosted version, it'd be very helpful if there were an option to zero-pad the file names based on seconds times so that they sort correctly.

i.e. instead of:

0.png
10.5.png
5.5.png

they came out as:

00.0.png
05.5.png
10.5.png

I guess you'd have to work out the longest number of digits needed before and after the decimal point and pad to that.