Generate the \u{... ... ...} form

[r12a]

from Mark Davis:

I really like the [Separate]! I think it would be best as [Compact ☑️]
and as a top-level check box. That would be very handy for outputing the
compact form of \x and \u, eg \x{61 9 62} instead of \x{61}\x{9}\x{62}.
I suggest the default be unchecked.

Generating the \u{... ... ...} form is somewhat complicated, and i don't think i'll have time to figure out how best to do it for this go around, but i'll bear it in mind for future updates.