Read at most 1 KiB or 50 lines of a file and render the attributed string in a bitmap context.
The theme is set to Mac Classic to ensure a white background for best look when the previews are used as icons in Finder.
The user’s default fixed width font in size 4 is used. With this font size only around 7 lines are shown, so we need to make it smaller, but we probably want to scale down the result to allow fractional line heights.
A lot of code is copy/pasted from the QuickLook preview generator.
This was suggested in pull request #1226. Ideally we would make the limit flexible, e.g. see how much we can generate in 1-2 seconds, but that is a non-trivial change, so the fixed limit will do for now, and while truncated data is suboptimal, it’s better than being killed due to QL manager’s timeout.
UTIs are taken from both the Apple supplied list and newly created for those that didn't exist. For those languages where no clear 'owner' existed to provide the reverse-DNS notation we use a com.macromates.* stand-in.
