Determine feasibilty of transitions

[ItMightBeKaraoke]

Look into the various transitions in KBP and determine which can be implemented reasonably.

• Fade transition could be achieved by lining up the start and end times on pages. I think KBS also does things like a screen clear before fade in to avoid glitching. We don't have the glitching problem, but may want to avoid unexpected overlap and adjust the end times on the previous page for fade ins, and the next page for fade outs.
• Clear screen transition is like fade but with fade of 0
• Some of the wipes could possibly be done with \t and \clip applied to every line on the page at the same time
• Movement based can use \move
• The other shape wipes probably can't be reasonably done in .ass and would need to be added afterward.
• Line by line could be emulated with multiple lines and \kf (transparent to first color, first color to second color, second color to transparent). To make it extra authentic, it would need a queue, so multiple lines aren't loading in/out at the same time.

Then there's the matter of what options to make available to control these. There should at least be an option to keep the current behavior ignoring transitions, but possibly additional settings are needed between that and the most faithful reproduction of transitions.

[ItMightBeKaraoke]

As a special case, any transitions based on rectangles could potentially use \clip/\iclip with \t, but unfortunately that wouldn't work for circle or other shapes.