Automatically detect Fountain-type files by Scene Heading pattern

[chuangcaleb]

Performance concerns

Still means I'll be parsing every note in the background to detect the Scene Heading regex/text pattern match, once every keystroke.

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that is a great idea, I must confess. I could also just make it run the initial Fountain-or-not checks once every n number of seconds
where n is configurable, but running a regex check once every 5 seconds isn't that computationally expensive also

Credit: Discord#Thomsem