Both were defined as explode | map(...) | implode, which took 4 seconds
on a 10 MB string, about 90 times as long as parsing it.
Change the case of A-Z or a-z a byte at a time in C, copying multibyte
UTF-8 sequences unchanged, so the output stays the same and the 10 MB
case now takes about 60 ms including parsing. On a non-string input the
error now names the function, "ascii_downcase input must be a string",
instead of "explode input must be a string".
Michiel van Slobbe
864d769d88