Function lowercase_first

crawl-ref/source/stringutil.cc:88–97

Warning: this (and uppercase_first()) relies on no libc (glibc, BSD libc, MSVC crt) supporting letters that expand or contract, like German ß (-> SS) upon capitalization / lowercasing. This is mostly a fault of the API -- there's no way to return two characters in one code point. Also, all characters must have the same length in bytes before and after lowercasing, all platforms currently have this

// A non-hacky version would be slower for no gain other than sane code; at
// least unless you use some more powerful API.
string lowercase_first(string s)
{
    char32_t c;
    if (!s.empty())
    {
        utf8towc(&c, &s[0]);
        wctoutf8(&s[0], towlower(c));
    }
    return s;
}

string uppercase_first(string s)
{