Randomly Chosen Variable Time Delays for Slideshows

[TheDoktar]

This pull request adds some additional syntax to the -D option or --slideshow-delay option. The new code is fully backward compatible with the old syntax and definition of the -D option. The old syntax allowed a real number which gave the slide delay in seconds, with - to start in pauused mode and 0 meaning a perpetual delay. For example -D 10 Would give a new slide every 10 seconds.

The syntax is extended in two way. First a comma seperated list of numbers may be used for example -D 5,10,20 would give equal probability of delays of 5, 10 and 20 seconds. Duplicates are allowed so that -D 5,5,5,10,20 would give 3 chances of a 5 second delay and one of 10 seconds and one of 20.

Each number may optionially include a multiplier so that the above can also be written: -D 5x3,10,20 As before a leading - is interpreted as start in paused mode.