Most notably, it now detects all-lowercase files and returns these
as-is. The tests have been expanded with two cases and are now used
as a benchmark (admittedly a rather trivial one).
name old time/op new time/op delta
UnicodeLowercaseMaybeChange-8 4.59µs ± 2% 4.57µs ± 1% ~ (p=0.197 n=10+10)
UnicodeLowercaseNoChange-8 3.26µs ± 1% 3.09µs ± 1% -5.27% (p=0.000 n=9+10)
greatroar
3e24d82513