use sds.{h,c} from hiredis (see #5)

With it we can replace the former tokenizer but we can also
re-format string replies which are not simple ASCII strings
(this occurs e.g with SETBIT) thanks to `sdscatrepr`.

See redis/src/redis-cli.c `cliFormatReplyTTY` for more
details.
sds.{h,c}: missing `const`-s
compile with `-Wall -Werror`
lua-ios.mk: build Lua with -Os
README: typo
upgrade fakeredis.lua