This is a special third kind of structure found in Unicode, besides
singletons and ranges.
This dramatically reduces the number of explicit singletons in the
lookup tables.
Also, I changed the awk-script so that it can sort trivial
translations as well, breaking down the LOC even more.
The binary size of tr dropped from 67K to 51K.
Previously, the to*rune function would have to jiggle with two
arrays, and it somehow evaded me that it is actually way simpler
to just add another entry to the arrays if needed.
Binary size goes slightly down, e.g. tr statically linked against
musl: 68072 -> 67688
Behind the scenes though the conversion should be a bit faster and,
more importantly, the scary case-conversion function is simplified
and easier to understand.
It also drops nearly half the LOC in upperrune.c and lowerrune.c.
This optimizes the binary size for each tool that uses these functions.
Previously, if a program just used one single function, maybe even a
one-liner, it would statically compile in all lookup-tables, bloating
the binary by up to 20K.
All these changes are derived from a local libutf where I do the
primary changes. So I hope that I can merge these things into libutf
sooner or later, as discussed on the ml.
